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/vmc_ns/ram.rs

@@ -0,0 +1,28 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RAM {
+    #[doc = "0x00 - Description cluster: RAM\\[n\\]
+power control register"]
+    pub power: POWER,
+    #[doc = "0x04 - Description cluster: RAM\\[n\\]
+power control set register"]
+    pub powerset: POWERSET,
+    #[doc = "0x08 - Description cluster: RAM\\[n\\]
+power control clear register"]
+    pub powerclr: POWERCLR,
+}
+#[doc = "POWER (rw) register accessor: an alias for `Reg<POWER_SPEC>`"]
+pub type POWER = crate::Reg<power::POWER_SPEC>;
+#[doc = "Description cluster: RAM\\[n\\]
+power control register"]
+pub mod power;
+#[doc = "POWERSET (rw) register accessor: an alias for `Reg<POWERSET_SPEC>`"]
+pub type POWERSET = crate::Reg<powerset::POWERSET_SPEC>;
+#[doc = "Description cluster: RAM\\[n\\]
+power control set register"]
+pub mod powerset;
+#[doc = "POWERCLR (rw) register accessor: an alias for `Reg<POWERCLR_SPEC>`"]
+pub type POWERCLR = crate::Reg<powerclr::POWERCLR_SPEC>;
+#[doc = "Description cluster: RAM\\[n\\]
+power control clear register"]
+pub mod powerclr;