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/nrf52811-pac/src/twim0/psel.rs

@@ -0,0 +1,16 @@
+#[doc = r"Register block"]
+#[repr(C)]
+pub struct PSEL {
+    #[doc = "0x00 - Pin select for SCL signal"]
+    pub scl: SCL,
+    #[doc = "0x04 - Pin select for SDA signal"]
+    pub sda: SDA,
+}
+#[doc = "SCL (rw) register accessor: an alias for `Reg<SCL_SPEC>`"]
+pub type SCL = crate::Reg<scl::SCL_SPEC>;
+#[doc = "Pin select for SCL signal"]
+pub mod scl;
+#[doc = "SDA (rw) register accessor: an alias for `Reg<SDA_SPEC>`"]
+pub type SDA = crate::Reg<sda::SDA_SPEC>;
+#[doc = "Pin select for SDA signal"]
+pub mod sda;