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/nrf9120-pac/src/ficr_s.rs

@@ -0,0 +1,36 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RegisterBlock {
+    _reserved0: [u8; 0x0140],
+    #[doc = "0x140..0x14c - SIP-specific device info"]
+    pub sipinfo: SIPINFO,
+    _reserved1: [u8; 0xb4],
+    #[doc = "0x200..0x22c - Device info"]
+    pub info: INFO,
+    _reserved2: [u8; 0xd4],
+    #[doc = "0x300..0xb00 - Unspecified"]
+    pub trimcnf: [TRIMCNF; 256],
+    _reserved3: [u8; 0x0100],
+    #[doc = "0xc00..0xc20 - NIST800-90B RNG calibration data"]
+    pub trng90b: TRNG90B,
+}
+#[doc = "SIP-specific device info"]
+pub use sipinfo::SIPINFO;
+#[doc = r"Cluster"]
+#[doc = "SIP-specific device info"]
+pub mod sipinfo;
+#[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 = "NIST800-90B RNG calibration data"]
+pub use trng90b::TRNG90B;
+#[doc = r"Cluster"]
+#[doc = "NIST800-90B RNG calibration data"]
+pub mod trng90b;