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/nrf51-pac/src/uicr/xtalfreq.rs

@@ -0,0 +1,129 @@
+#[doc = "Register `XTALFREQ` reader"]
+pub struct R(crate::R<XTALFREQ_SPEC>);
+impl core::ops::Deref for R {
+    type Target = crate::R<XTALFREQ_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl From<crate::R<XTALFREQ_SPEC>> for R {
+    #[inline(always)]
+    fn from(reader: crate::R<XTALFREQ_SPEC>) -> Self {
+        R(reader)
+    }
+}
+#[doc = "Register `XTALFREQ` writer"]
+pub struct W(crate::W<XTALFREQ_SPEC>);
+impl core::ops::Deref for W {
+    type Target = crate::W<XTALFREQ_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl core::ops::DerefMut for W {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+impl From<crate::W<XTALFREQ_SPEC>> for W {
+    #[inline(always)]
+    fn from(writer: crate::W<XTALFREQ_SPEC>) -> Self {
+        W(writer)
+    }
+}
+#[doc = "Field `XTALFREQ` reader - Reset value for CLOCK XTALFREQ register."]
+pub type XTALFREQ_R = crate::FieldReader<u8, XTALFREQ_A>;
+#[doc = "Reset value for CLOCK XTALFREQ register.\n\nValue on reset: 255"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[repr(u8)]
+pub enum XTALFREQ_A {
+    #[doc = "255: 16MHz Xtal is used."]
+    _16MHZ = 255,
+    #[doc = "0: 32MHz Xtal is used."]
+    _32MHZ = 0,
+}
+impl From<XTALFREQ_A> for u8 {
+    #[inline(always)]
+    fn from(variant: XTALFREQ_A) -> Self {
+        variant as _
+    }
+}
+impl XTALFREQ_R {
+    #[doc = "Get enumerated values variant"]
+    #[inline(always)]
+    pub fn variant(&self) -> Option<XTALFREQ_A> {
+        match self.bits {
+            255 => Some(XTALFREQ_A::_16MHZ),
+            0 => Some(XTALFREQ_A::_32MHZ),
+            _ => None,
+        }
+    }
+    #[doc = "Checks if the value of the field is `_16MHZ`"]
+    #[inline(always)]
+    pub fn is_16mhz(&self) -> bool {
+        *self == XTALFREQ_A::_16MHZ
+    }
+    #[doc = "Checks if the value of the field is `_32MHZ`"]
+    #[inline(always)]
+    pub fn is_32mhz(&self) -> bool {
+        *self == XTALFREQ_A::_32MHZ
+    }
+}
+#[doc = "Field `XTALFREQ` writer - Reset value for CLOCK XTALFREQ register."]
+pub type XTALFREQ_W<'a, const O: u8> =
+    crate::FieldWriter<'a, u32, XTALFREQ_SPEC, u8, XTALFREQ_A, 8, O>;
+impl<'a, const O: u8> XTALFREQ_W<'a, O> {
+    #[doc = "16MHz Xtal is used."]
+    #[inline(always)]
+    pub fn _16mhz(self) -> &'a mut W {
+        self.variant(XTALFREQ_A::_16MHZ)
+    }
+    #[doc = "32MHz Xtal is used."]
+    #[inline(always)]
+    pub fn _32mhz(self) -> &'a mut W {
+        self.variant(XTALFREQ_A::_32MHZ)
+    }
+}
+impl R {
+    #[doc = "Bits 0:7 - Reset value for CLOCK XTALFREQ register."]
+    #[inline(always)]
+    pub fn xtalfreq(&self) -> XTALFREQ_R {
+        XTALFREQ_R::new((self.bits & 0xff) as u8)
+    }
+}
+impl W {
+    #[doc = "Bits 0:7 - Reset value for CLOCK XTALFREQ register."]
+    #[inline(always)]
+    pub fn xtalfreq(&mut self) -> XTALFREQ_W<0> {
+        XTALFREQ_W::new(self)
+    }
+    #[doc = "Writes raw bits to the register."]
+    #[inline(always)]
+    pub unsafe fn bits(&mut self, bits: u32) -> &mut Self {
+        self.0.bits(bits);
+        self
+    }
+}
+#[doc = "Reset value for CLOCK XTALFREQ register.\n\nThis register you can [`read`](crate::generic::Reg::read), [`write_with_zero`](crate::generic::Reg::write_with_zero), [`reset`](crate::generic::Reg::reset), [`write`](crate::generic::Reg::write), [`modify`](crate::generic::Reg::modify). See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [xtalfreq](index.html) module"]
+pub struct XTALFREQ_SPEC;
+impl crate::RegisterSpec for XTALFREQ_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [xtalfreq::R](R) reader structure"]
+impl crate::Readable for XTALFREQ_SPEC {
+    type Reader = R;
+}
+#[doc = "`write(|w| ..)` method takes [xtalfreq::W](W) writer structure"]
+impl crate::Writable for XTALFREQ_SPEC {
+    type Writer = W;
+}
+#[doc = "`reset()` method sets XTALFREQ to value 0xffff_ffff"]
+impl crate::Resettable for XTALFREQ_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0xffff_ffff
+    }
+}