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/rng.rs

@@ -0,0 +1,18 @@
+#[repr(C)]
+#[cfg_attr(feature = "impl-register-debug", derive(Debug))]
+#[doc = "Register block"]
+pub struct RegisterBlock {
+    _reserved0: [u8; 0x0110],
+    data: DATA,
+}
+impl RegisterBlock {
+    #[doc = "0x110 - Random number data"]
+    #[inline(always)]
+    pub const fn data(&self) -> &DATA {
+        &self.data
+    }
+}
+#[doc = "DATA (r) register accessor: Random number data\n\nYou can [`read`](crate::Reg::read) this register and get [`data::R`]. See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [`mod@data`] module"]
+pub type DATA = crate::Reg<data::DATA_SPEC>;
+#[doc = "Random number data"]
+pub mod data;