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_load.rs

@@ -0,0 +1,32 @@
+#[doc = "Register `UNIT%s_LOAD` writer"]
+pub type W = crate::W<UNIT_LOAD_SPEC>;
+#[doc = "Field `LOAD` writer - timer unit0 sync enable signal"]
+pub type LOAD_W<'a, REG> = crate::BitWriter<'a, REG>;
+#[cfg(feature = "impl-register-debug")]
+impl core::fmt::Debug for crate::generic::Reg<UNIT_LOAD_SPEC> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "(not readable)")
+    }
+}
+impl W {
+    #[doc = "Bit 0 - timer unit0 sync enable signal"]
+    #[inline(always)]
+    pub fn load(&mut self) -> LOAD_W<UNIT_LOAD_SPEC> {
+        LOAD_W::new(self, 0)
+    }
+}
+#[doc = "system timer unit%s conf sync register\n\nYou can [`reset`](crate::Reg::reset), [`write`](crate::Reg::write), [`write_with_zero`](crate::Reg::write_with_zero) this register using [`unit_load::W`](W). See [API](https://docs.rs/svd2rust/#read--modify--write-api)."]
+pub struct UNIT_LOAD_SPEC;
+impl crate::RegisterSpec for UNIT_LOAD_SPEC {
+    type Ux = u32;
+}
+#[doc = "`write(|w| ..)` method takes [`unit_load::W`](W) writer structure"]
+impl crate::Writable for UNIT_LOAD_SPEC {
+    type Safety = crate::Unsafe;
+    const ZERO_TO_MODIFY_FIELDS_BITMAP: u32 = 0;
+    const ONE_TO_MODIFY_FIELDS_BITMAP: u32 = 0;
+}
+#[doc = "`reset()` method sets UNIT%s_LOAD to value 0"]
+impl crate::Resettable for UNIT_LOAD_SPEC {
+    const RESET_VALUE: u32 = 0;
+}