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/esp32s3/src/systimer/unit_value.rs

@@ -0,0 +1,27 @@
+#[repr(C)]
+#[cfg_attr(feature = "impl-register-debug", derive(Debug))]
+#[doc = "Cluster UNIT%s_VALUE, containing UNIT?_VALUE_HI, UNIT?_VALUE_LO"]
+pub struct UNIT_VALUE {
+    hi: HI,
+    lo: LO,
+}
+impl UNIT_VALUE {
+    #[doc = "0x00 - system timer unit0 value high register"]
+    #[inline(always)]
+    pub const fn hi(&self) -> &HI {
+        &self.hi
+    }
+    #[doc = "0x04 - system timer unit0 value low register"]
+    #[inline(always)]
+    pub const fn lo(&self) -> &LO {
+        &self.lo
+    }
+}
+#[doc = "HI (r) register accessor: system timer unit0 value high register\n\nYou can [`read`](crate::Reg::read) this register and get [`hi::R`]. See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [`mod@hi`] module"]
+pub type HI = crate::Reg<hi::HI_SPEC>;
+#[doc = "system timer unit0 value high register"]
+pub mod hi;
+#[doc = "LO (r) register accessor: system timer unit0 value low register\n\nYou can [`read`](crate::Reg::read) this register and get [`lo::R`]. See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [`mod@lo`] module"]
+pub type LO = crate::Reg<lo::LO_SPEC>;
+#[doc = "system timer unit0 value low register"]
+pub mod lo;