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/kmu_ns.rs

@@ -0,0 +1,68 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct RegisterBlock {
+    #[doc = "0x00 - Push a key slot over secure APB"]
+    pub tasks_push_keyslot: TASKS_PUSH_KEYSLOT,
+    _reserved1: [u8; 0xfc],
+    #[doc = "0x100 - Key slot successfully pushed over secure APB"]
+    pub events_keyslot_pushed: EVENTS_KEYSLOT_PUSHED,
+    #[doc = "0x104 - Key slot has been revoked and cannot be tasked for selection"]
+    pub events_keyslot_revoked: EVENTS_KEYSLOT_REVOKED,
+    #[doc = "0x108 - No key slot selected, no destination address defined, or error during push operation"]
+    pub events_keyslot_error: EVENTS_KEYSLOT_ERROR,
+    _reserved4: [u8; 0x01f4],
+    #[doc = "0x300 - Enable or disable interrupt"]
+    pub inten: INTEN,
+    #[doc = "0x304 - Enable interrupt"]
+    pub intenset: INTENSET,
+    #[doc = "0x308 - Disable interrupt"]
+    pub intenclr: INTENCLR,
+    #[doc = "0x30c - Pending interrupts"]
+    pub intpend: INTPEND,
+    _reserved8: [u8; 0xfc],
+    #[doc = "0x40c - Status bits for KMU operation"]
+    pub status: STATUS,
+    _reserved9: [u8; 0xf0],
+    #[doc = "0x500 - Select key slot to be read over AHB or pushed over secure APB when TASKS_PUSH_KEYSLOT is started"]
+    pub selectkeyslot: SELECTKEYSLOT,
+}
+#[doc = "TASKS_PUSH_KEYSLOT (w) register accessor: an alias for `Reg<TASKS_PUSH_KEYSLOT_SPEC>`"]
+pub type TASKS_PUSH_KEYSLOT = crate::Reg<tasks_push_keyslot::TASKS_PUSH_KEYSLOT_SPEC>;
+#[doc = "Push a key slot over secure APB"]
+pub mod tasks_push_keyslot;
+#[doc = "EVENTS_KEYSLOT_PUSHED (rw) register accessor: an alias for `Reg<EVENTS_KEYSLOT_PUSHED_SPEC>`"]
+pub type EVENTS_KEYSLOT_PUSHED = crate::Reg<events_keyslot_pushed::EVENTS_KEYSLOT_PUSHED_SPEC>;
+#[doc = "Key slot successfully pushed over secure APB"]
+pub mod events_keyslot_pushed;
+#[doc = "EVENTS_KEYSLOT_REVOKED (rw) register accessor: an alias for `Reg<EVENTS_KEYSLOT_REVOKED_SPEC>`"]
+pub type EVENTS_KEYSLOT_REVOKED = crate::Reg<events_keyslot_revoked::EVENTS_KEYSLOT_REVOKED_SPEC>;
+#[doc = "Key slot has been revoked and cannot be tasked for selection"]
+pub mod events_keyslot_revoked;
+#[doc = "EVENTS_KEYSLOT_ERROR (rw) register accessor: an alias for `Reg<EVENTS_KEYSLOT_ERROR_SPEC>`"]
+pub type EVENTS_KEYSLOT_ERROR = crate::Reg<events_keyslot_error::EVENTS_KEYSLOT_ERROR_SPEC>;
+#[doc = "No key slot selected, no destination address defined, or error during push operation"]
+pub mod events_keyslot_error;
+#[doc = "INTEN (rw) register accessor: an alias for `Reg<INTEN_SPEC>`"]
+pub type INTEN = crate::Reg<inten::INTEN_SPEC>;
+#[doc = "Enable or disable interrupt"]
+pub mod inten;
+#[doc = "INTENSET (rw) register accessor: an alias for `Reg<INTENSET_SPEC>`"]
+pub type INTENSET = crate::Reg<intenset::INTENSET_SPEC>;
+#[doc = "Enable interrupt"]
+pub mod intenset;
+#[doc = "INTENCLR (rw) register accessor: an alias for `Reg<INTENCLR_SPEC>`"]
+pub type INTENCLR = crate::Reg<intenclr::INTENCLR_SPEC>;
+#[doc = "Disable interrupt"]
+pub mod intenclr;
+#[doc = "INTPEND (r) register accessor: an alias for `Reg<INTPEND_SPEC>`"]
+pub type INTPEND = crate::Reg<intpend::INTPEND_SPEC>;
+#[doc = "Pending interrupts"]
+pub mod intpend;
+#[doc = "STATUS (r) register accessor: an alias for `Reg<STATUS_SPEC>`"]
+pub type STATUS = crate::Reg<status::STATUS_SPEC>;
+#[doc = "Status bits for KMU operation"]
+pub mod status;
+#[doc = "SELECTKEYSLOT (rw) register accessor: an alias for `Reg<SELECTKEYSLOT_SPEC>`"]
+pub type SELECTKEYSLOT = crate::Reg<selectkeyslot::SELECTKEYSLOT_SPEC>;
+#[doc = "Select key slot to be read over AHB or pushed over secure APB when TASKS_PUSH_KEYSLOT is started"]
+pub mod selectkeyslot;