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/nrf5340-app-pac/src/tad_s.rs

@@ -0,0 +1,37 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RegisterBlock {
+    _reserved0: [u8; 0x04],
+    #[doc = "0x04 - Start all trace and debug clocks."]
+    pub clockstart: CLOCKSTART,
+    #[doc = "0x08 - Stop all trace and debug clocks."]
+    pub clockstop: CLOCKSTOP,
+    _reserved2: [u8; 0x04f4],
+    #[doc = "0x500 - Enable debug domain and aquire selected GPIOs"]
+    pub enable: ENABLE,
+    #[doc = "0x504..0x518 - Unspecified"]
+    pub psel: PSEL,
+    #[doc = "0x518 - Clocking options for the Trace Port debug interface Reset behavior is the same as debug components"]
+    pub traceportspeed: TRACEPORTSPEED,
+}
+#[doc = "CLOCKSTART (w) register accessor: an alias for `Reg<CLOCKSTART_SPEC>`"]
+pub type CLOCKSTART = crate::Reg<clockstart::CLOCKSTART_SPEC>;
+#[doc = "Start all trace and debug clocks."]
+pub mod clockstart;
+#[doc = "CLOCKSTOP (w) register accessor: an alias for `Reg<CLOCKSTOP_SPEC>`"]
+pub type CLOCKSTOP = crate::Reg<clockstop::CLOCKSTOP_SPEC>;
+#[doc = "Stop all trace and debug clocks."]
+pub mod clockstop;
+#[doc = "ENABLE (rw) register accessor: an alias for `Reg<ENABLE_SPEC>`"]
+pub type ENABLE = crate::Reg<enable::ENABLE_SPEC>;
+#[doc = "Enable debug domain and aquire selected GPIOs"]
+pub mod enable;
+#[doc = "Unspecified"]
+pub use psel::PSEL;
+#[doc = r"Cluster"]
+#[doc = "Unspecified"]
+pub mod psel;
+#[doc = "TRACEPORTSPEED (rw) register accessor: an alias for `Reg<TRACEPORTSPEED_SPEC>`"]
+pub type TRACEPORTSPEED = crate::Reg<traceportspeed::TRACEPORTSPEED_SPEC>;
+#[doc = "Clocking options for the Trace Port debug interface Reset behavior is the same as debug components"]
+pub mod traceportspeed;