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/pinned_drop/conditional-drop-impl.stderr

@@ -0,0 +1,34 @@
+error[E0367]: `Drop` impl requires `T: Unpin` but the struct it is implemented for does not
+  --> tests/ui/pinned_drop/conditional-drop-impl.rs:11:9
+   |
+11 | impl<T: Unpin> Drop for DropImpl<T> {
+   |         ^^^^^
+   |
+note: the implementor must specify the same requirement
+  --> tests/ui/pinned_drop/conditional-drop-impl.rs:7:1
+   |
+ 7 | struct DropImpl<T> {
+   | ^^^^^^^^^^^^^^^^^^
+
+error[E0367]: `Drop` impl requires `T: Unpin` but the struct it is implemented for does not
+  --> tests/ui/pinned_drop/conditional-drop-impl.rs:16:1
+   |
+16 | / pin_project! {
+17 | |     //~^ ERROR E0367
+18 | |     struct PinnedDropImpl<T> {
+19 | |         #[pin]
+...  |
+26 | | }
+   | |_^
+   |
+note: the implementor must specify the same requirement
+  --> tests/ui/pinned_drop/conditional-drop-impl.rs:16:1
+   |
+16 | / pin_project! {
+17 | |     //~^ ERROR E0367
+18 | |     struct PinnedDropImpl<T> {
+19 | |         #[pin]
+...  |
+26 | | }
+   | |_^
+   = 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)