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/nrf52805-pac/src/ficr/temp/b3.rs

@@ -0,0 +1,40 @@
+#[doc = "Register `B3` reader"]
+pub struct R(crate::R<B3_SPEC>);
+impl core::ops::Deref for R {
+    type Target = crate::R<B3_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl From<crate::R<B3_SPEC>> for R {
+    #[inline(always)]
+    fn from(reader: crate::R<B3_SPEC>) -> Self {
+        R(reader)
+    }
+}
+#[doc = "Field `B` reader - B (y-intercept)"]
+pub type B_R = crate::FieldReader<u16, u16>;
+impl R {
+    #[doc = "Bits 0:13 - B (y-intercept)"]
+    #[inline(always)]
+    pub fn b(&self) -> B_R {
+        B_R::new((self.bits & 0x3fff) as u16)
+    }
+}
+#[doc = "Y-intercept B3\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 [b3](index.html) module"]
+pub struct B3_SPEC;
+impl crate::RegisterSpec for B3_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [b3::R](R) reader structure"]
+impl crate::Readable for B3_SPEC {
+    type Reader = R;
+}
+#[doc = "`reset()` method sets B3 to value 0xffff_ffff"]
+impl crate::Resettable for B3_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0xffff_ffff
+    }
+}