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/spis0/semstat.rs

@@ -0,0 +1,92 @@
+#[doc = "Register `SEMSTAT` reader"]
+pub struct R(crate::R<SEMSTAT_SPEC>);
+impl core::ops::Deref for R {
+    type Target = crate::R<SEMSTAT_SPEC>;
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl From<crate::R<SEMSTAT_SPEC>> for R {
+    #[inline(always)]
+    fn from(reader: crate::R<SEMSTAT_SPEC>) -> Self {
+        R(reader)
+    }
+}
+#[doc = "Field `SEMSTAT` reader - Semaphore status"]
+pub type SEMSTAT_R = crate::FieldReader<u8, SEMSTAT_A>;
+#[doc = "Semaphore status\n\nValue on reset: 1"]
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[repr(u8)]
+pub enum SEMSTAT_A {
+    #[doc = "0: Semaphore is free"]
+    FREE = 0,
+    #[doc = "1: Semaphore is assigned to CPU"]
+    CPU = 1,
+    #[doc = "2: Semaphore is assigned to SPI slave"]
+    SPIS = 2,
+    #[doc = "3: Semaphore is assigned to SPI but a handover to the CPU is pending"]
+    CPUPENDING = 3,
+}
+impl From<SEMSTAT_A> for u8 {
+    #[inline(always)]
+    fn from(variant: SEMSTAT_A) -> Self {
+        variant as _
+    }
+}
+impl SEMSTAT_R {
+    #[doc = "Get enumerated values variant"]
+    #[inline(always)]
+    pub fn variant(&self) -> SEMSTAT_A {
+        match self.bits {
+            0 => SEMSTAT_A::FREE,
+            1 => SEMSTAT_A::CPU,
+            2 => SEMSTAT_A::SPIS,
+            3 => SEMSTAT_A::CPUPENDING,
+            _ => unreachable!(),
+        }
+    }
+    #[doc = "Checks if the value of the field is `FREE`"]
+    #[inline(always)]
+    pub fn is_free(&self) -> bool {
+        *self == SEMSTAT_A::FREE
+    }
+    #[doc = "Checks if the value of the field is `CPU`"]
+    #[inline(always)]
+    pub fn is_cpu(&self) -> bool {
+        *self == SEMSTAT_A::CPU
+    }
+    #[doc = "Checks if the value of the field is `SPIS`"]
+    #[inline(always)]
+    pub fn is_spis(&self) -> bool {
+        *self == SEMSTAT_A::SPIS
+    }
+    #[doc = "Checks if the value of the field is `CPUPENDING`"]
+    #[inline(always)]
+    pub fn is_cpupending(&self) -> bool {
+        *self == SEMSTAT_A::CPUPENDING
+    }
+}
+impl R {
+    #[doc = "Bits 0:1 - Semaphore status"]
+    #[inline(always)]
+    pub fn semstat(&self) -> SEMSTAT_R {
+        SEMSTAT_R::new((self.bits & 3) as u8)
+    }
+}
+#[doc = "Semaphore status register\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 [semstat](index.html) module"]
+pub struct SEMSTAT_SPEC;
+impl crate::RegisterSpec for SEMSTAT_SPEC {
+    type Ux = u32;
+}
+#[doc = "`read()` method returns [semstat::R](R) reader structure"]
+impl crate::Readable for SEMSTAT_SPEC {
+    type Reader = R;
+}
+#[doc = "`reset()` method sets SEMSTAT to value 0x01"]
+impl crate::Resettable for SEMSTAT_SPEC {
+    #[inline(always)]
+    fn reset_value() -> Self::Ux {
+        0x01
+    }
+}