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/nrf9120-pac/src/generic/raw.rs

@@ -0,0 +1,93 @@
+use super::{marker, BitM, FieldSpec, RegisterSpec, Unsafe, Writable};
+pub struct R<REG: RegisterSpec> {
+    pub(crate) bits: REG::Ux,
+    pub(super) _reg: marker::PhantomData<REG>,
+}
+pub struct W<REG: RegisterSpec> {
+    #[doc = "Writable bits"]
+    pub(crate) bits: REG::Ux,
+    pub(super) _reg: marker::PhantomData<REG>,
+}
+pub struct FieldReader<FI = u8>
+where
+    FI: FieldSpec,
+{
+    pub(crate) bits: FI::Ux,
+    _reg: marker::PhantomData<FI>,
+}
+impl<FI: FieldSpec> FieldReader<FI> {
+    #[doc = " Creates a new instance of the reader."]
+    #[allow(unused)]
+    #[inline(always)]
+    pub(crate) const fn new(bits: FI::Ux) -> Self {
+        Self {
+            bits,
+            _reg: marker::PhantomData,
+        }
+    }
+}
+pub struct BitReader<FI = bool> {
+    pub(crate) bits: bool,
+    _reg: marker::PhantomData<FI>,
+}
+impl<FI> BitReader<FI> {
+    #[doc = " Creates a new instance of the reader."]
+    #[allow(unused)]
+    #[inline(always)]
+    pub(crate) const fn new(bits: bool) -> Self {
+        Self {
+            bits,
+            _reg: marker::PhantomData,
+        }
+    }
+}
+pub struct FieldWriter<'a, REG, const WI: u8, FI = u8, Safety = Unsafe>
+where
+    REG: Writable + RegisterSpec,
+    FI: FieldSpec,
+{
+    pub(crate) w: &'a mut W<REG>,
+    pub(crate) o: u8,
+    _field: marker::PhantomData<(FI, Safety)>,
+}
+impl<'a, REG, const WI: u8, FI, Safety> FieldWriter<'a, REG, WI, FI, Safety>
+where
+    REG: Writable + RegisterSpec,
+    FI: FieldSpec,
+{
+    #[doc = " Creates a new instance of the writer"]
+    #[allow(unused)]
+    #[inline(always)]
+    pub(crate) fn new(w: &'a mut W<REG>, o: u8) -> Self {
+        Self {
+            w,
+            o,
+            _field: marker::PhantomData,
+        }
+    }
+}
+pub struct BitWriter<'a, REG, FI = bool, M = BitM>
+where
+    REG: Writable + RegisterSpec,
+    bool: From<FI>,
+{
+    pub(crate) w: &'a mut W<REG>,
+    pub(crate) o: u8,
+    _field: marker::PhantomData<(FI, M)>,
+}
+impl<'a, REG, FI, M> BitWriter<'a, REG, FI, M>
+where
+    REG: Writable + RegisterSpec,
+    bool: From<FI>,
+{
+    #[doc = " Creates a new instance of the writer"]
+    #[allow(unused)]
+    #[inline(always)]
+    pub(crate) fn new(w: &'a mut W<REG>, o: u8) -> Self {
+        Self {
+            w,
+            o,
+            _field: marker::PhantomData,
+        }
+    }
+}