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/sha/mode.rs

@@ -0,0 +1,45 @@
+#[doc = "Register `MODE` reader"]
+pub type R = crate::R<MODE_SPEC>;
+#[doc = "Register `MODE` writer"]
+pub type W = crate::W<MODE_SPEC>;
+#[doc = "Field `MODE` reader - sha mode"]
+pub type MODE_R = crate::FieldReader;
+#[doc = "Field `MODE` writer - sha mode"]
+pub type MODE_W<'a, REG> = crate::FieldWriter<'a, REG, 3>;
+impl R {
+    #[doc = "Bits 0:2 - sha mode"]
+    #[inline(always)]
+    pub fn mode(&self) -> MODE_R {
+        MODE_R::new((self.bits & 7) as u8)
+    }
+}
+#[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("MODE").field("mode", &self.mode()).finish()
+    }
+}
+impl W {
+    #[doc = "Bits 0:2 - sha mode"]
+    #[inline(always)]
+    pub fn mode(&mut self) -> MODE_W<MODE_SPEC> {
+        MODE_W::new(self, 0)
+    }
+}
+#[doc = "Initial configuration register.\n\nYou can [`read`](crate::Reg::read) this register and get [`mode::R`](R). You can [`reset`](crate::Reg::reset), [`write`](crate::Reg::write), [`write_with_zero`](crate::Reg::write_with_zero) this register using [`mode::W`](W). You can also [`modify`](crate::Reg::modify) this register. See [API](https://docs.rs/svd2rust/#read--modify--write-api)."]
+pub struct MODE_SPEC;
+impl crate::RegisterSpec for MODE_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [`mode::R`](R) reader structure"]
+impl crate::Readable for MODE_SPEC {}
+#[doc = "`write(|w| ..)` method takes [`mode::W`](W) writer structure"]
+impl crate::Writable for MODE_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 MODE to value 0"]
+impl crate::Resettable for MODE_SPEC {
+    const RESET_VALUE: u32 = 0;
+}