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/pin-project-lite/tests/ui/pin_project/conflict-drop.stderr

@@ -0,0 +1,15 @@
+error[E0119]: conflicting implementations of trait `MustNotImplDrop` for type `Foo<_, _>`
+  --> tests/ui/pin_project/conflict-drop.rs:5:1
+   |
+ 5 | / pin_project! { //~ ERROR E0119
+ 6 | |     struct Foo<T, U> {
+ 7 | |         #[pin]
+ 8 | |         future: T,
+...  |
+11 | | }
+   | | ^
+   | | |
+   | |_first implementation here
+   |   conflicting implementation for `Foo<_, _>`
+   |
+   = note: this error originates in the macro `$crate::__pin_project_make_drop_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)