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/ficr_s.rs

@@ -0,0 +1,42 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RegisterBlock {
+    _reserved0: [u8; 0x0200],
+    #[doc = "0x200..0x22c - Device info"]
+    pub info: INFO,
+    _reserved1: [u8; 0xd4],
+    #[doc = "0x300..0x400 - Unspecified"]
+    pub trimcnf: [TRIMCNF; 32],
+    _reserved2: [u8; 0x50],
+    #[doc = "0x450..0x460 - Unspecified"]
+    pub nfc: NFC,
+    _reserved3: [u8; 0x07a0],
+    #[doc = "0xc00..0xc20 - NIST800-90B RNG calibration data"]
+    pub trng90b: TRNG90B,
+    #[doc = "0xc20 - XOSC32M capacitor selection trim values"]
+    pub xosc32mtrim: XOSC32MTRIM,
+}
+#[doc = "Device info"]
+pub use info::INFO;
+#[doc = r"Cluster"]
+#[doc = "Device info"]
+pub mod info;
+#[doc = "Unspecified"]
+pub use trimcnf::TRIMCNF;
+#[doc = r"Cluster"]
+#[doc = "Unspecified"]
+pub mod trimcnf;
+#[doc = "Unspecified"]
+pub use nfc::NFC;
+#[doc = r"Cluster"]
+#[doc = "Unspecified"]
+pub mod nfc;
+#[doc = "NIST800-90B RNG calibration data"]
+pub use trng90b::TRNG90B;
+#[doc = r"Cluster"]
+#[doc = "NIST800-90B RNG calibration data"]
+pub mod trng90b;
+#[doc = "XOSC32MTRIM (r) register accessor: an alias for `Reg<XOSC32MTRIM_SPEC>`"]
+pub type XOSC32MTRIM = crate::Reg<xosc32mtrim::XOSC32MTRIM_SPEC>;
+#[doc = "XOSC32M capacitor selection trim values"]
+pub mod xosc32mtrim;