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/efuse/rd_usr_data2.rs

@@ -0,0 +1,30 @@
+#[doc = "Register `RD_USR_DATA2` reader"]
+pub type R = crate::R<RD_USR_DATA2_SPEC>;
+#[doc = "Field `USR_DATA2` reader - Stores the second 32 bits of BLOCK3 (user)."]
+pub type USR_DATA2_R = crate::FieldReader<u32>;
+impl R {
+    #[doc = "Bits 0:31 - Stores the second 32 bits of BLOCK3 (user)."]
+    #[inline(always)]
+    pub fn usr_data2(&self) -> USR_DATA2_R {
+        USR_DATA2_R::new(self.bits)
+    }
+}
+#[cfg(feature = "impl-register-debug")]
+impl core::fmt::Debug for R {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        f.debug_struct("RD_USR_DATA2")
+            .field("usr_data2", &self.usr_data2())
+            .finish()
+    }
+}
+#[doc = "Register 2 of BLOCK3 (user).\n\nYou can [`read`](crate::Reg::read) this register and get [`rd_usr_data2::R`](R). See [API](https://docs.rs/svd2rust/#read--modify--write-api)."]
+pub struct RD_USR_DATA2_SPEC;
+impl crate::RegisterSpec for RD_USR_DATA2_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [`rd_usr_data2::R`](R) reader structure"]
+impl crate::Readable for RD_USR_DATA2_SPEC {}
+#[doc = "`reset()` method sets RD_USR_DATA2 to value 0"]
+impl crate::Resettable for RD_USR_DATA2_SPEC {
+    const RESET_VALUE: u32 = 0;
+}