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-net-pac/src/ficr_ns.rs

@@ -0,0 +1,45 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RegisterBlock {
+    _reserved0: [u8; 0x0200],
+    #[doc = "0x200..0x22c - Device info"]
+    pub info: INFO,
+    _reserved1: [u8; 0x54],
+    #[doc = "0x280..0x290 - Description collection: Encryption Root, word n"]
+    pub er: [ER; 4],
+    #[doc = "0x290..0x2a0 - Description collection: Identity Root, word n"]
+    pub ir: [IR; 4],
+    #[doc = "0x2a0 - Device address type"]
+    pub deviceaddrtype: DEVICEADDRTYPE,
+    #[doc = "0x2a4..0x2ac - Description collection: Device address n"]
+    pub deviceaddr: [DEVICEADDR; 2],
+    _reserved5: [u8; 0x54],
+    #[doc = "0x300..0x400 - Unspecified"]
+    pub trimcnf: [TRIMCNF; 32],
+}
+#[doc = "Device info"]
+pub use info::INFO;
+#[doc = r"Cluster"]
+#[doc = "Device info"]
+pub mod info;
+#[doc = "ER (r) register accessor: an alias for `Reg<ER_SPEC>`"]
+pub type ER = crate::Reg<er::ER_SPEC>;
+#[doc = "Description collection: Encryption Root, word n"]
+pub mod er;
+#[doc = "IR (r) register accessor: an alias for `Reg<IR_SPEC>`"]
+pub type IR = crate::Reg<ir::IR_SPEC>;
+#[doc = "Description collection: Identity Root, word n"]
+pub mod ir;
+#[doc = "DEVICEADDRTYPE (r) register accessor: an alias for `Reg<DEVICEADDRTYPE_SPEC>`"]
+pub type DEVICEADDRTYPE = crate::Reg<deviceaddrtype::DEVICEADDRTYPE_SPEC>;
+#[doc = "Device address type"]
+pub mod deviceaddrtype;
+#[doc = "DEVICEADDR (r) register accessor: an alias for `Reg<DEVICEADDR_SPEC>`"]
+pub type DEVICEADDR = crate::Reg<deviceaddr::DEVICEADDR_SPEC>;
+#[doc = "Description collection: Device address n"]
+pub mod deviceaddr;
+#[doc = "Unspecified"]
+pub use trimcnf::TRIMCNF;
+#[doc = r"Cluster"]
+#[doc = "Unspecified"]
+pub mod trimcnf;