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/nrf52820-pac/src/clock/hfclkstat.rs

@@ -0,0 +1,115 @@
+#[doc = "Register `HFCLKSTAT` reader"]
+pub struct R(crate::R<HFCLKSTAT_SPEC>);
+impl core::ops::Deref for R {
+    type Target = crate::R<HFCLKSTAT_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl From<crate::R<HFCLKSTAT_SPEC>> for R {
+    #[inline(always)]
+    fn from(reader: crate::R<HFCLKSTAT_SPEC>) -> Self {
+        R(reader)
+    }
+}
+#[doc = "Field `SRC` reader - Source of HFCLK"]
+pub type SRC_R = crate::BitReader<SRC_A>;
+#[doc = "Source of HFCLK\n\nValue on reset: 0"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum SRC_A {
+    #[doc = "0: 64 MHz internal oscillator (HFINT)"]
+    RC = 0,
+    #[doc = "1: 64 MHz crystal oscillator (HFXO)"]
+    XTAL = 1,
+}
+impl From<SRC_A> for bool {
+    #[inline(always)]
+    fn from(variant: SRC_A) -> Self {
+        variant as u8 != 0
+    }
+}
+impl SRC_R {
+    #[doc = "Get enumerated values variant"]
+    #[inline(always)]
+    pub fn variant(&self) -> SRC_A {
+        match self.bits {
+            false => SRC_A::RC,
+            true => SRC_A::XTAL,
+        }
+    }
+    #[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 = "Field `STATE` reader - HFCLK state"]
+pub type STATE_R = crate::BitReader<STATE_A>;
+#[doc = "HFCLK state\n\nValue on reset: 0"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum STATE_A {
+    #[doc = "0: HFCLK not running"]
+    NOT_RUNNING = 0,
+    #[doc = "1: HFCLK running"]
+    RUNNING = 1,
+}
+impl From<STATE_A> for bool {
+    #[inline(always)]
+    fn from(variant: STATE_A) -> Self {
+        variant as u8 != 0
+    }
+}
+impl STATE_R {
+    #[doc = "Get enumerated values variant"]
+    #[inline(always)]
+    pub fn variant(&self) -> STATE_A {
+        match self.bits {
+            false => STATE_A::NOT_RUNNING,
+            true => STATE_A::RUNNING,
+        }
+    }
+    #[doc = "Checks if the value of the field is `NOT_RUNNING`"]
+    #[inline(always)]
+    pub fn is_not_running(&self) -> bool {
+        *self == STATE_A::NOT_RUNNING
+    }
+    #[doc = "Checks if the value of the field is `RUNNING`"]
+    #[inline(always)]
+    pub fn is_running(&self) -> bool {
+        *self == STATE_A::RUNNING
+    }
+}
+impl R {
+    #[doc = "Bit 0 - Source of HFCLK"]
+    #[inline(always)]
+    pub fn src(&self) -> SRC_R {
+        SRC_R::new((self.bits & 1) != 0)
+    }
+    #[doc = "Bit 16 - HFCLK state"]
+    #[inline(always)]
+    pub fn state(&self) -> STATE_R {
+        STATE_R::new(((self.bits >> 16) & 1) != 0)
+    }
+}
+#[doc = "HFCLK status\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 [hfclkstat](index.html) module"]
+pub struct HFCLKSTAT_SPEC;
+impl crate::RegisterSpec for HFCLKSTAT_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [hfclkstat::R](R) reader structure"]
+impl crate::Readable for HFCLKSTAT_SPEC {
+    type Reader = R;
+}
+#[doc = "`reset()` method sets HFCLKSTAT to value 0"]
+impl crate::Resettable for HFCLKSTAT_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0
+    }
+}