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/invalid.stderr

@@ -0,0 +1,47 @@
+error: no rules expected `(`
+ --> tests/ui/pin_project/invalid.rs:7:14
+  |
+7 |         #[pin()] //~ ERROR no rules expected the token `(`
+  |              ^ no rules expected this token in macro call
+  |
+note: while trying to match `]`
+ --> src/lib.rs
+  |
+  |                 $(#[$pin:ident])?
+  |                               ^
+
+error: no rules expected `(`
+ --> tests/ui/pin_project/invalid.rs:7:14
+  |
+7 |         #[pin()] //~ ERROR no rules expected the token `(`
+  |              ^ no rules expected this token in macro call
+  |
+note: while trying to match `]`
+ --> src/lib.rs
+  |
+  |                 $(#[$pin:ident])?
+  |                               ^
+
+error: no rules expected `#`
+  --> tests/ui/pin_project/invalid.rs:22:9
+   |
+22 |         #[pin] //~ ERROR no rules expected the token `#`
+   |         ^ no rules expected this token in macro call
+   |
+note: while trying to match meta-variable `$field_vis:vis`
+  --> src/lib.rs
+   |
+   |                 $field_vis:vis $field:ident: $field_ty:ty
+   |                 ^^^^^^^^^^^^^^
+
+error: no rules expected `#`
+  --> tests/ui/pin_project/invalid.rs:22:9
+   |
+22 |         #[pin] //~ ERROR no rules expected the token `#`
+   |         ^ no rules expected this token in macro call
+   |
+note: while trying to match meta-variable `$field_vis:vis`
+  --> src/lib.rs
+   |
+   |                 $field_vis:vis $field:ident: $field_ty:ty
+   |                 ^^^^^^^^^^^^^^