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/mwu/region.rs

@@ -0,0 +1,16 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct REGION {
+    #[doc = "0x00 - Description cluster\\[0\\]: Start address for region 0"]
+    pub start: START,
+    #[doc = "0x04 - Description cluster\\[0\\]: End address of region 0"]
+    pub end: END,
+}
+#[doc = "START (rw) register accessor: an alias for `Reg<START_SPEC>`"]
+pub type START = crate::Reg<start::START_SPEC>;
+#[doc = "Description cluster\\[0\\]: Start address for region 0"]
+pub mod start;
+#[doc = "END (rw) register accessor: an alias for `Reg<END_SPEC>`"]
+pub type END = crate::Reg<end::END_SPEC>;
+#[doc = "Description cluster\\[0\\]: End address of region 0"]
+pub mod end;