feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/esp-build/.cargo-checksum.json

@@ -0,0 +1 @@
+{"files":{".cargo_vcs_info.json":"0e6b992e514296b611341a199f76d70f8796fd447a47de504601bd5a233dbe7d","Cargo.toml":"c40a61fe9acf33383c437cd9bcf4c92fe72b5ae35c0b51349df0c84d4bed828d","Cargo.toml.orig":"47cdc66d69a3ee0573ff08420bfab4c59055dd92cc0c1deca9331707f2adec9b","README.md":"2ba51541849f8935a3f65c14bccb1d6aec0b1dcf54ac1dd951eccdb434804611","src/lib.rs":"bc7661aa9017889a8e85363509d92de46730226faa5a30bd5c4f84dc20528422"},"package":"b94a4b8d74e7cc7baabcca5b2277b41877e039ad9cd49959d48ef94dac7eab4b"}

vendor/esp-build/.cargo_vcs_info.json

@@ -0,0 +1,6 @@
+{
+  "git": {
+    "sha1": "111dcda1032562503bfe2de87401683c680e505f"
+  },
+  "path_in_vcs": "esp-build"
+}

vendor/esp-build/Cargo.toml

@@ -0,0 +1,36 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2021"
+rust-version = "1.60.0"
+name = "esp-build"
+version = "0.1.0"
+description = "Build utilities for esp-hal"
+readme = "README.md"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/esp-rs/esp-hal"
+
+[lib]
+proc-macro = true
+
+[dependencies.quote]
+version = "1.0.35"
+
+[dependencies.syn]
+version = "2.0.52"
+features = [
+    "fold",
+    "full",
+]
+
+[dependencies.termcolor]
+version = "1.4.1"

vendor/esp-build/README.md

@@ -0,0 +1,33 @@
+# esp-build
+
+[![Crates.io](https://img.shields.io/crates/v/esp-build?labelColor=1C2C2E&color=C96329&logo=Rust&style=flat-square)](https://crates.io/crates/esp-build)
+[![docs.rs](https://img.shields.io/docsrs/esp-build?labelColor=1C2C2E&color=C96329&logo=rust&style=flat-square)](https://docs.rs/esp-build)
+![MSRV](https://img.shields.io/badge/MSRV-1.60-blue?labelColor=1C2C2E&style=flat-square)
+![Crates.io](https://img.shields.io/crates/l/esp-build?labelColor=1C2C2E&style=flat-square)
+[![Matrix](https://img.shields.io/matrix/esp-rs:matrix.org?label=join%20matrix&labelColor=1C2C2E&color=BEC5C9&logo=matrix&style=flat-square)](https://matrix.to/#/#esp-rs:matrix.org)
+
+Build utilities for use with `esp-hal` and other related packages, intended for use in [build scripts]. This package is still quite minimal, but provides:
+
+[build scripts]: https://doc.rust-lang.org/cargo/reference/build-scripts.html
+
+## [Documentation](https://docs.rs/crate/esp-build)
+
+## Minimum Supported Rust Version (MSRV)
+
+This crate is guaranteed to compile on stable Rust 1.60 and up. It _might_
+compile with older versions but that may change in any new patch release.
+
+## License
+
+Licensed under either of:
+
+- Apache License, Version 2.0 ([LICENSE-APACHE](../LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+- MIT license ([LICENSE-MIT](../LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in
+the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without
+any additional terms or conditions.

vendor/esp-build/src/lib.rs

@@ -0,0 +1,222 @@
+//! Build utilities for esp-hal.
+
+#![doc(html_logo_url = "https://avatars.githubusercontent.com/u/46717278")]
+
+use std::{io::Write as _, process};
+
+use proc_macro::TokenStream;
+use syn::{parse_macro_input, punctuated::Punctuated, LitStr, Token};
+use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
+
+/// Print a build error and terminate the process.
+///
+/// It should be noted that the error will be printed BEFORE the main function
+/// is called, and as such this should NOT be thought analogous to `println!` or
+/// similar utilities.
+///
+/// ## Example
+///
+/// ```rust
+/// esp_build::error! {"
+/// ERROR: something really bad has happened!
+/// "}
+/// // Process exits with exit code 1
+/// ```
+#[proc_macro]
+pub fn error(input: TokenStream) -> TokenStream {
+    do_alert(Color::Red, input);
+    process::exit(1);
+}
+
+/// Print a build warning.
+///
+/// It should be noted that the warning will be printed BEFORE the main function
+/// is called, and as such this should NOT be thought analogous to `println!` or
+/// similar utilities.
+///
+/// ## Example
+///
+/// ```rust
+/// esp_build::warning! {"
+/// WARNING: something unpleasant has happened!
+/// "};
+/// ```
+#[proc_macro]
+pub fn warning(input: TokenStream) -> TokenStream {
+    do_alert(Color::Yellow, input)
+}
+
+/// Given some features, assert that **at most** one of the features is enabled.
+///
+/// ## Example
+/// ```rust
+/// assert_unique_features!("foo", "bar", "baz");
+/// ```
+#[proc_macro]
+pub fn assert_unique_features(input: TokenStream) -> TokenStream {
+    let features = parse_macro_input!(input with Punctuated<LitStr, Token![,]>::parse_terminated)
+        .into_iter()
+        .collect::<Vec<_>>();
+
+    let pairs = unique_pairs(&features);
+    let unique_cfgs = pairs
+        .iter()
+        .map(|(a, b)| quote::quote! { all(feature = #a, feature = #b) });
+
+    let message = format!(
+        r#"
+ERROR: expected exactly zero or one enabled feature from feature group:
+  {:?}
+"#,
+        features.iter().map(|lit| lit.value()).collect::<Vec<_>>(),
+    );
+
+    quote::quote! {
+        #[cfg(any(#(#unique_cfgs),*))]
+        ::esp_build::error! { #message }
+    }
+    .into()
+}
+
+/// Given some features, assert that **at least** one of the features is
+/// enabled.
+///
+/// ## Example
+/// ```rust
+/// assert_used_features!("foo", "bar", "baz");
+/// ```
+#[proc_macro]
+pub fn assert_used_features(input: TokenStream) -> TokenStream {
+    let features = parse_macro_input!(input with Punctuated<LitStr, Token![,]>::parse_terminated)
+        .into_iter()
+        .collect::<Vec<_>>();
+
+    let message = format!(
+        r#"
+ERROR: expected at least one enabled feature from feature group:
+  {:?}
+    "#,
+        features.iter().map(|lit| lit.value()).collect::<Vec<_>>()
+    );
+
+    quote::quote! {
+        #[cfg(not(any(#(feature = #features),*)))]
+        ::esp_build::error! { #message }
+    }
+    .into()
+}
+
+/// Given some features, assert that **exactly** one of the features is enabled.
+///
+/// ## Example
+/// ```rust
+/// assert_unique_used_features!("foo", "bar", "baz");
+/// ```
+#[proc_macro]
+pub fn assert_unique_used_features(input: TokenStream) -> TokenStream {
+    let features = parse_macro_input!(input with Punctuated<LitStr, Token![,]>::parse_terminated)
+        .into_iter()
+        .collect::<Vec<_>>();
+
+    let pairs = unique_pairs(&features);
+    let unique_cfgs = pairs
+        .iter()
+        .map(|(a, b)| quote::quote! { all(feature = #a, feature = #b) });
+
+    let message = format!(
+        r#"
+ERROR: expected exactly one enabled feature from feature group:
+  {:?}
+    "#,
+        features.iter().map(|lit| lit.value()).collect::<Vec<_>>()
+    );
+
+    quote::quote! {
+        #[cfg(any(any(#(#unique_cfgs),*), not(any(#(feature = #features),*))))]
+        ::esp_build::error! { #message }
+    }
+    .into()
+}
+
+// ----------------------------------------------------------------------------
+// Helper Functions
+
+// Adapted from:
+// https://github.com/dtolnay/build-alert/blob/49d060e/src/lib.rs#L54-L93
+fn do_alert(color: Color, input: TokenStream) -> TokenStream {
+    let message = parse_macro_input!(input as LitStr).value();
+
+    let ref mut stderr = StandardStream::stderr(ColorChoice::Auto);
+    let color_spec = ColorSpec::new().set_fg(Some(color)).clone();
+
+    let mut has_nonspace = false;
+
+    for mut line in message.lines() {
+        if !has_nonspace {
+            let (maybe_heading, rest) = split_heading(line);
+
+            if let Some(heading) = maybe_heading {
+                stderr.set_color(color_spec.clone().set_bold(true)).ok();
+                write!(stderr, "\n{}", heading).ok();
+                has_nonspace = true;
+            }
+
+            line = rest;
+        }
+
+        if line.is_empty() {
+            writeln!(stderr).ok();
+        } else {
+            stderr.set_color(&color_spec).ok();
+            writeln!(stderr, "{}", line).ok();
+
+            has_nonspace = has_nonspace || line.contains(|ch: char| ch != ' ');
+        }
+    }
+
+    stderr.reset().ok();
+    writeln!(stderr).ok();
+
+    TokenStream::new()
+}
+
+// Adapted from:
+// https://github.com/dtolnay/build-alert/blob/49d060e/src/lib.rs#L95-L114
+fn split_heading(s: &str) -> (Option<&str>, &str) {
+    let mut end = 0;
+    while end < s.len() && s[end..].starts_with(|ch: char| ch.is_ascii_uppercase()) {
+        end += 1;
+    }
+
+    if end >= 3 && (end == s.len() || s[end..].starts_with(':')) {
+        let (heading, rest) = s.split_at(end);
+        (Some(heading), rest)
+    } else {
+        (None, s)
+    }
+}
+
+fn unique_pairs(features: &Vec<LitStr>) -> Vec<(&LitStr, &LitStr)> {
+    let mut pairs = Vec::new();
+
+    let mut i = 0;
+    let mut j = 0;
+
+    while i < features.len() {
+        let a = &features[i];
+        let b = &features[j];
+
+        if a.value() != b.value() {
+            pairs.push((a, b));
+        }
+
+        j += 1;
+
+        if j >= features.len() {
+            i += 1;
+            j = i;
+        }
+    }
+
+    pairs
+}