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/rustversion/build/build.rs

@@ -0,0 +1,114 @@
+#![allow(
+    clippy::elidable_lifetime_names,
+    clippy::enum_glob_use,
+    clippy::must_use_candidate,
+    clippy::single_match_else
+)]
+
+mod rustc;
+
+use std::env;
+use std::ffi::OsString;
+use std::fmt::{self, Debug, Display};
+use std::fs;
+use std::iter;
+use std::path::Path;
+use std::process::{self, Command};
+
+fn main() {
+    println!("cargo:rerun-if-changed=build/build.rs");
+
+    let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
+    let rustc_wrapper = env::var_os("RUSTC_WRAPPER").filter(|wrapper| !wrapper.is_empty());
+    let wrapped_rustc = rustc_wrapper.iter().chain(iter::once(&rustc));
+
+    let mut is_clippy_driver = false;
+    let mut is_mirai = false;
+    let version = loop {
+        let mut command;
+        if is_mirai {
+            command = Command::new(&rustc);
+        } else {
+            let mut wrapped_rustc = wrapped_rustc.clone();
+            command = Command::new(wrapped_rustc.next().unwrap());
+            command.args(wrapped_rustc);
+        }
+        if is_clippy_driver {
+            command.arg("--rustc");
+        }
+        command.arg("--version");
+
+        let output = match command.output() {
+            Ok(output) => output,
+            Err(e) => {
+                let rustc = rustc.to_string_lossy();
+                eprintln!("Error: failed to run `{} --version`: {}", rustc, e);
+                process::exit(1);
+            }
+        };
+
+        let string = match String::from_utf8(output.stdout) {
+            Ok(string) => string,
+            Err(e) => {
+                let rustc = rustc.to_string_lossy();
+                eprintln!(
+                    "Error: failed to parse output of `{} --version`: {}",
+                    rustc, e,
+                );
+                process::exit(1);
+            }
+        };
+
+        break match rustc::parse(&string) {
+            rustc::ParseResult::Success(version) => version,
+            rustc::ParseResult::OopsClippy if !is_clippy_driver => {
+                is_clippy_driver = true;
+                continue;
+            }
+            rustc::ParseResult::OopsMirai if !is_mirai && rustc_wrapper.is_some() => {
+                is_mirai = true;
+                continue;
+            }
+            rustc::ParseResult::Unrecognized
+            | rustc::ParseResult::OopsClippy
+            | rustc::ParseResult::OopsMirai => {
+                eprintln!(
+                    "Error: unexpected output from `rustc --version`: {:?}\n\n\
+                    Please file an issue in https://github.com/dtolnay/rustversion",
+                    string
+                );
+                process::exit(1);
+            }
+        };
+    };
+
+    if version.minor < 38 {
+        // Prior to 1.38, a #[proc_macro] is not allowed to be named `cfg`.
+        println!("cargo:rustc-cfg=cfg_macro_not_allowed");
+    }
+
+    if version.minor >= 80 {
+        println!("cargo:rustc-check-cfg=cfg(cfg_macro_not_allowed)");
+        println!("cargo:rustc-check-cfg=cfg(host_os, values(\"windows\"))");
+    }
+
+    let version = format!("{:#}\n", Render(&version));
+    let out_dir = env::var_os("OUT_DIR").expect("OUT_DIR not set");
+    let out_file = Path::new(&out_dir).join("version.expr");
+    fs::write(out_file, version).expect("failed to write version.expr");
+
+    let host = env::var_os("HOST").expect("HOST not set");
+    if let Some("windows") = host.to_str().unwrap().split('-').nth(2) {
+        println!("cargo:rustc-cfg=host_os=\"windows\"");
+    }
+}
+
+// Shim Version's {:?} format into a {} format, because {:?} is unusable in
+// format strings when building with `-Zfmt-debug=none`.
+struct Render<'a>(&'a rustc::Version);
+
+impl<'a> Display for Render<'a> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        Debug::fmt(self.0, formatter)
+    }
+}

vendor/rustversion/build/rustc.rs

@@ -0,0 +1,126 @@
+use self::Channel::*;
+use std::fmt::{self, Debug};
+
+pub enum ParseResult {
+    Success(Version),
+    OopsClippy,
+    OopsMirai,
+    Unrecognized,
+}
+
+#[cfg_attr(test, derive(PartialEq))]
+pub struct Version {
+    pub minor: u16,
+    pub patch: u16,
+    pub channel: Channel,
+}
+
+#[cfg_attr(test, derive(PartialEq))]
+pub enum Channel {
+    Stable,
+    Beta,
+    Nightly(Date),
+    Dev,
+}
+
+#[cfg_attr(test, derive(PartialEq))]
+pub struct Date {
+    pub year: u16,
+    pub month: u8,
+    pub day: u8,
+}
+
+pub fn parse(string: &str) -> ParseResult {
+    let last_line = string.lines().last().unwrap_or(string);
+    let mut words = last_line.trim().split(' ');
+
+    match words.next() {
+        Some("rustc") => {}
+        Some(word) if word.starts_with("clippy") => return ParseResult::OopsClippy,
+        Some("mirai") => return ParseResult::OopsMirai,
+        Some(_) | None => return ParseResult::Unrecognized,
+    }
+
+    parse_words(&mut words).map_or(ParseResult::Unrecognized, ParseResult::Success)
+}
+
+fn parse_words(words: &mut dyn Iterator<Item = &str>) -> Option<Version> {
+    let mut version_channel = words.next()?.split('-');
+    let version = version_channel.next()?;
+    let channel = version_channel.next();
+
+    let mut digits = version.split('.');
+    let major = digits.next()?;
+    if major != "1" {
+        return None;
+    }
+    let minor = digits.next()?.parse().ok()?;
+    let patch = digits.next().unwrap_or("0").parse().ok()?;
+
+    let channel = match channel {
+        None => Stable,
+        Some("dev") => Dev,
+        Some(channel) if channel.starts_with("beta") => Beta,
+        Some("nightly") => match words.next() {
+            Some(hash) if hash.starts_with('(') => match words.next() {
+                None if hash.ends_with(')') => Dev,
+                Some(date) if date.ends_with(')') => {
+                    let mut date = date[..date.len() - 1].split('-');
+                    let year = date.next()?.parse().ok()?;
+                    let month = date.next()?.parse().ok()?;
+                    let day = date.next()?.parse().ok()?;
+                    match date.next() {
+                        None => Nightly(Date { year, month, day }),
+                        Some(_) => return None,
+                    }
+                }
+                None | Some(_) => return None,
+            },
+            Some(_) => return None,
+            None => Dev,
+        },
+        Some(_) => return None,
+    };
+
+    Some(Version {
+        minor,
+        patch,
+        channel,
+    })
+}
+
+impl Debug for Version {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("crate::version::Version")
+            .field("minor", &self.minor)
+            .field("patch", &self.patch)
+            .field("channel", &self.channel)
+            .finish()
+    }
+}
+
+impl Debug for Channel {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Channel::Stable => formatter.write_str("crate::version::Channel::Stable"),
+            Channel::Beta => formatter.write_str("crate::version::Channel::Beta"),
+            Channel::Nightly(date) => formatter
+                .debug_tuple("crate::version::Channel::Nightly")
+                .field(date)
+                .finish(),
+            Channel::Dev => formatter.write_str("crate::version::Channel::Dev"),
+        }
+    }
+}
+
+impl Debug for Date {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("crate::date::Date")
+            .field("year", &self.year)
+            .field("month", &self.month)
+            .field("day", &self.day)
+            .finish()
+    }
+}