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/fugit/src/helpers.rs

@@ -0,0 +1,80 @@
+/// Needed due to not being allowed to call const-fn in `PartialEq` fo some reasion
+/// get the error:
+///
+/// ```console
+/// error[E0401]: can't use generic parameters from outer function
+///   --> src/main.rs:25:47
+///    |
+/// 21 | impl<const L_NOM: u32, const L_DENOM: u32, const R_NOM: u32, const R_DENOM: u32>
+///    |                                                                    ------- const parameter from outer function
+/// ...
+/// 25 |         const TEST: u32 = gcd_binary_u32(L_DENOM, R_DENOM);
+///    |                                                   ^^^^^^^ use of generic parameter from outer function
+///
+/// For more information about this error, try `rustc --explain E0401`
+/// ```
+pub struct Helpers<const L_NOM: u32, const L_DENOM: u32, const R_NOM: u32, const R_DENOM: u32>;
+
+impl<const L_NOM: u32, const L_DENOM: u32, const R_NOM: u32, const R_DENOM: u32>
+    Helpers<L_NOM, L_DENOM, R_NOM, R_DENOM>
+{
+    /// Helper constants generated at compile time
+    pub const DIVISOR: u64 =
+        gcd::binary_u64(L_DENOM as u64 * R_NOM as u64, R_DENOM as u64 * L_NOM as u64);
+
+    /// Helper constants generated at compile time
+    pub const DIVISOR_2: u64 =
+        gcd::binary_u64(L_NOM as u64 * R_NOM as u64, R_DENOM as u64 * L_DENOM as u64);
+
+    /// Helper constants generated at compile time for Durations
+    pub const RD_TIMES_LN: u64 = (R_DENOM as u64 * L_NOM as u64) / Self::DIVISOR;
+
+    /// Helper constants generated at compile time
+    pub const LD_TIMES_RN: u64 = (L_DENOM as u64 * R_NOM as u64) / Self::DIVISOR;
+
+    /// Helper constants generated at compile time for Rates
+    pub const LN_TIMES_RN: u64 = (L_NOM as u64 * R_NOM as u64) / Self::DIVISOR_2;
+
+    /// Helper constants generated at compile time for Rates
+    pub const RD_TIMES_LD: u64 = (R_DENOM as u64 * L_DENOM as u64) / Self::DIVISOR_2;
+
+    /// Helper constants generated at compile time for Rates
+    pub const RATE_TO_DURATION_NUMERATOR: u64 = Self::RD_TIMES_LD / Self::LN_TIMES_RN;
+
+    /// Helper constants generated at compile time
+    pub const SAME_BASE: bool = Self::LD_TIMES_RN == Self::RD_TIMES_LN;
+}
+
+#[allow(dead_code)]
+#[allow(path_statements)]
+pub(crate) const fn greater_than_0<const N: u32>() {
+    Assert::<N, 0>::GREATER;
+}
+
+#[allow(dead_code)]
+/// Const assert hack
+pub struct Assert<const L: u32, const R: u32>;
+
+#[allow(dead_code)]
+impl<const L: u32, const R: u32> Assert<L, R> {
+    /// Const assert hack
+    pub const GREATER_EQ: () = assert!(L >= R);
+
+    /// Const assert hack
+    pub const LESS_EQ: () = assert!(L <= R);
+
+    /// Const assert hack
+    pub const NOT_EQ: () = assert!(L != R);
+
+    /// Const assert hack
+    pub const EQ: () = assert!(L == R);
+
+    /// Const assert hack
+    pub const GREATER: () = assert!(L > R);
+
+    /// Const assert hack
+    pub const LESS: () = assert!(L < R);
+
+    /// Const assert hack
+    pub const POWER_OF_TWO: () = assert!(L.is_power_of_two());
+}