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/nrf9160-pac/src/wdt_ns/rr.rs

@@ -0,0 +1,73 @@
+#[doc = "Register `RR[%s]` writer"]
+pub struct W(crate::W<RR_SPEC>);
+impl core::ops::Deref for W {
+    type Target = crate::W<RR_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<RR_SPEC>> for W {
+    #[inline(always)]
+    fn from(writer: crate::W<RR_SPEC>) -> Self {
+        W(writer)
+    }
+}
+#[doc = "Reload request register\n\nValue on reset: 0"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[repr(u32)]
+pub enum RR_AW {
+    #[doc = "1850885685: Value to request a reload of the watchdog timer"]
+    RELOAD = 1850885685,
+}
+impl From<RR_AW> for u32 {
+    #[inline(always)]
+    fn from(variant: RR_AW) -> Self {
+        variant as _
+    }
+}
+#[doc = "Field `RR` writer - Reload request register"]
+pub type RR_W<'a, const O: u8> = crate::FieldWriter<'a, u32, RR_SPEC, u32, RR_AW, 32, O>;
+impl<'a, const O: u8> RR_W<'a, O> {
+    #[doc = "Value to request a reload of the watchdog timer"]
+    #[inline(always)]
+    pub fn reload(self) -> &'a mut W {
+        self.variant(RR_AW::RELOAD)
+    }
+}
+impl W {
+    #[doc = "Bits 0:31 - Reload request register"]
+    #[inline(always)]
+    pub fn rr(&mut self) -> RR_W<0> {
+        RR_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 = "Description collection: Reload request n\n\nThis register you can [`write_with_zero`](crate::generic::Reg::write_with_zero), [`reset`](crate::generic::Reg::reset), [`write`](crate::generic::Reg::write). See [API](https://docs.rs/svd2rust/#read--modify--write-api).\n\nFor information about available fields see [rr](index.html) module"]
+pub struct RR_SPEC;
+impl crate::RegisterSpec for RR_SPEC {
+    type Ux = u32;
+}
+#[doc = "`write(|w| ..)` method takes [rr::W](W) writer structure"]
+impl crate::Writable for RR_SPEC {
+    type Writer = W;
+}
+#[doc = "`reset()` method sets RR[%s]
+to value 0"]
+impl crate::Resettable for RR_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0
+    }
+}