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/nrf52811-pac/src/pdm/psel.rs

@@ -0,0 +1,16 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct PSEL {
+    #[doc = "0x00 - Pin number configuration for PDM CLK signal"]
+    pub clk: CLK,
+    #[doc = "0x04 - Pin number configuration for PDM DIN signal"]
+    pub din: DIN,
+}
+#[doc = "CLK (rw) register accessor: an alias for `Reg<CLK_SPEC>`"]
+pub type CLK = crate::Reg<clk::CLK_SPEC>;
+#[doc = "Pin number configuration for PDM CLK signal"]
+pub mod clk;
+#[doc = "DIN (rw) register accessor: an alias for `Reg<DIN_SPEC>`"]
+pub type DIN = crate::Reg<din::DIN_SPEC>;
+#[doc = "Pin number configuration for PDM DIN signal"]
+pub mod din;