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/nrf52840-pac/src/clock/lfclksrccopy.rs

@@ -0,0 +1,84 @@
+#[doc = "Register `LFCLKSRCCOPY` reader"]
+pub struct R(crate::R<LFCLKSRCCOPY_SPEC>);
+impl core::ops::Deref for R {
+    type Target = crate::R<LFCLKSRCCOPY_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl From<crate::R<LFCLKSRCCOPY_SPEC>> for R {
+    #[inline(always)]
+    fn from(reader: crate::R<LFCLKSRCCOPY_SPEC>) -> Self {
+        R(reader)
+    }
+}
+#[doc = "Field `SRC` reader - Clock source"]
+pub type SRC_R = crate::FieldReader<u8, SRC_A>;
+#[doc = "Clock source\n\nValue on reset: 0"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[repr(u8)]
+pub enum SRC_A {
+    #[doc = "0: 32.768 kHz RC oscillator (LFRC)"]
+    RC = 0,
+    #[doc = "1: 32.768 kHz crystal oscillator (LFXO)"]
+    XTAL = 1,
+    #[doc = "2: 32.768 kHz synthesized from HFCLK (LFSYNT)"]
+    SYNTH = 2,
+}
+impl From<SRC_A> for u8 {
+    #[inline(always)]
+    fn from(variant: SRC_A) -> Self {
+        variant as _
+    }
+}
+impl SRC_R {
+    #[doc = "Get enumerated values variant"]
+    #[inline(always)]
+    pub fn variant(&self) -> Option<SRC_A> {
+        match self.bits {
+            0 => Some(SRC_A::RC),
+            1 => Some(SRC_A::XTAL),
+            2 => Some(SRC_A::SYNTH),
+            _ => None,
+        }
+    }
+    #[doc = "Checks if the value of the field is `RC`"]
+    #[inline(always)]
+    pub fn is_rc(&self) -> bool {
+        *self == SRC_A::RC
+    }
+    #[doc = "Checks if the value of the field is `XTAL`"]
+    #[inline(always)]
+    pub fn is_xtal(&self) -> bool {
+        *self == SRC_A::XTAL
+    }
+    #[doc = "Checks if the value of the field is `SYNTH`"]
+    #[inline(always)]
+    pub fn is_synth(&self) -> bool {
+        *self == SRC_A::SYNTH
+    }
+}
+impl R {
+    #[doc = "Bits 0:1 - Clock source"]
+    #[inline(always)]
+    pub fn src(&self) -> SRC_R {
+        SRC_R::new((self.bits & 3) as u8)
+    }
+}
+#[doc = "Copy of LFCLKSRC register, set when LFCLKSTART task was triggered\n\nThis register you can [`read`](crate::generic::Reg::read). See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [lfclksrccopy](index.html) module"]
+pub struct LFCLKSRCCOPY_SPEC;
+impl crate::RegisterSpec for LFCLKSRCCOPY_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [lfclksrccopy::R](R) reader structure"]
+impl crate::Readable for LFCLKSRCCOPY_SPEC {
+    type Reader = R;
+}
+#[doc = "`reset()` method sets LFCLKSRCCOPY to value 0"]
+impl crate::Resettable for LFCLKSRCCOPY_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0
+    }
+}