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/darling_macro/.cargo-checksum.json

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vendor/darling_macro/.cargo_vcs_info.json

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+    "sha1": "f21aa2c5ccd002f978a18758815bd7e7cdba4741"
+  },
+  "path_in_vcs": "macro"
+}

vendor/darling_macro/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "darling_core"
+version = "0.21.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1247195ecd7e3c85f83c8d2a366e4210d588e802133e1e355180a9870b517ea4"
+dependencies = [
+ "fnv",
+ "ident_case",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "darling_macro"
+version = "0.21.3"
+dependencies = [
+ "darling_core",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "fnv"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
+
+[[package]]
+name = "ident_case"
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+checksum = "b9e0384b61958566e926dc50660321d12159025e767c18e043daf26b70104c39"
+
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+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "proc-macro2",
+]
+
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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vendor/darling_macro/Cargo.toml

@@ -0,0 +1,44 @@
+# 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 = "1.56"
+name = "darling_macro"
+version = "0.21.3"
+authors = ["Ted Driggs <ted.driggs@outlook.com>"]
+build = false
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = """
+Internal support for a proc-macro library for reading attributes into structs when
+implementing custom derives. Use https://crates.io/crates/darling in your code.
+"""
+readme = false
+license = "MIT"
+repository = "https://github.com/TedDriggs/darling"
+
+[lib]
+name = "darling_macro"
+path = "src/lib.rs"
+proc-macro = true
+
+[dependencies.darling_core]
+version = "=0.21.3"
+
+[dependencies.quote]
+version = "1.0.18"
+
+[dependencies.syn]
+version = "2.0.15"

vendor/darling_macro/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 Ted Driggs
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/darling_macro/src/lib.rs

@@ -0,0 +1,40 @@
+use darling_core::{derive, Error};
+use proc_macro::TokenStream;
+use syn::parse_macro_input;
+
+#[proc_macro_derive(FromMeta, attributes(darling))]
+pub fn derive_from_meta(input: TokenStream) -> TokenStream {
+    derive::from_meta(&parse_macro_input!(input)).into()
+}
+
+#[proc_macro_derive(FromMetaItem, attributes(darling))]
+pub fn derive_from_meta_item(_input: TokenStream) -> TokenStream {
+    Error::custom("darling::FromMetaItem has been replaced by darling::FromMeta")
+        .write_errors()
+        .into()
+}
+
+#[proc_macro_derive(FromAttributes, attributes(darling))]
+pub fn derive_from_attributes(input: TokenStream) -> TokenStream {
+    derive::from_attributes(&parse_macro_input!(input)).into()
+}
+
+#[proc_macro_derive(FromDeriveInput, attributes(darling))]
+pub fn derive_from_input(input: TokenStream) -> TokenStream {
+    derive::from_derive_input(&parse_macro_input!(input)).into()
+}
+
+#[proc_macro_derive(FromField, attributes(darling))]
+pub fn derive_field(input: TokenStream) -> TokenStream {
+    derive::from_field(&parse_macro_input!(input)).into()
+}
+
+#[proc_macro_derive(FromTypeParam, attributes(darling))]
+pub fn derive_type_param(input: TokenStream) -> TokenStream {
+    derive::from_type_param(&parse_macro_input!(input)).into()
+}
+
+#[proc_macro_derive(FromVariant, attributes(darling))]
+pub fn derive_variant(input: TokenStream) -> TokenStream {
+    derive::from_variant(&parse_macro_input!(input)).into()
+}