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/spim0_ns/iftiming.rs

@@ -0,0 +1,16 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct IFTIMING {
+    #[doc = "0x00 - Sample delay for input serial data on MISO"]
+    pub rxdelay: RXDELAY,
+    #[doc = "0x04 - Minimum duration between edge of CSN and edge of SCK and minimum duration CSN must stay high between transactions"]
+    pub csndur: CSNDUR,
+}
+#[doc = "RXDELAY (rw) register accessor: an alias for `Reg<RXDELAY_SPEC>`"]
+pub type RXDELAY = crate::Reg<rxdelay::RXDELAY_SPEC>;
+#[doc = "Sample delay for input serial data on MISO"]
+pub mod rxdelay;
+#[doc = "CSNDUR (rw) register accessor: an alias for `Reg<CSNDUR_SPEC>`"]
+pub type CSNDUR = crate::Reg<csndur::CSNDUR_SPEC>;
+#[doc = "Minimum duration between edge of CSN and edge of SCK and minimum duration CSN must stay high between transactions"]
+pub mod csndur;