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/nrf52832-pac/src/qdec/psel.rs

@@ -0,0 +1,22 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct PSEL {
+    #[doc = "0x00 - Pin select for LED signal"]
+    pub led: LED,
+    #[doc = "0x04 - Pin select for A signal"]
+    pub a: A,
+    #[doc = "0x08 - Pin select for B signal"]
+    pub b: B,
+}
+#[doc = "LED (rw) register accessor: an alias for `Reg<LED_SPEC>`"]
+pub type LED = crate::Reg<led::LED_SPEC>;
+#[doc = "Pin select for LED signal"]
+pub mod led;
+#[doc = "A (rw) register accessor: an alias for `Reg<A_SPEC>`"]
+pub type A = crate::Reg<a::A_SPEC>;
+#[doc = "Pin select for A signal"]
+pub mod a;
+#[doc = "B (rw) register accessor: an alias for `Reg<B_SPEC>`"]
+pub type B = crate::Reg<b::B_SPEC>;
+#[doc = "Pin select for B signal"]
+pub mod b;