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-unpin.stderr

@@ -0,0 +1,81 @@
+error[E0119]: conflicting implementations of trait `Unpin` for type `Foo<_, _>`
+  --> tests/ui/pin_project/conflict-unpin.rs:7:1
+   |
+ 7 | / pin_project! { //~ ERROR E0119
+ 8 | |     struct Foo<T, U> {
+ 9 | |         #[pin]
+10 | |         future: T,
+...  |
+13 | | }
+   | |_^ conflicting implementation for `Foo<_, _>`
+...
+16 |   impl<T, U> Unpin for Foo<T, U> where T: Unpin {} // Conditional Unpin impl
+   |   --------------------------------------------- first implementation here
+   |
+   = note: this error originates in the macro `$crate::__pin_project_make_unpin_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `Unpin` for type `Bar<_, _>`
+  --> tests/ui/pin_project/conflict-unpin.rs:20:1
+   |
+20 | / pin_project! { //~ ERROR E0119
+21 | |     struct Bar<T, U> {
+22 | |         #[pin]
+23 | |         future: T,
+...  |
+26 | | }
+   | |_^ conflicting implementation for `Bar<_, _>`
+...
+29 |   impl<T, U> Unpin for Bar<T, U> {} // Non-conditional Unpin impl
+   |   ------------------------------ first implementation here
+   |
+   = note: this error originates in the macro `$crate::__pin_project_make_unpin_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `Unpin` for type `Baz<_, _>`
+  --> tests/ui/pin_project/conflict-unpin.rs:31:1
+   |
+31 | / pin_project! { //~ ERROR E0119
+32 | |     struct Baz<T, U> {
+33 | |         #[pin]
+34 | |         future: T,
+...  |
+37 | | }
+   | |_^ conflicting implementation for `Baz<_, _>`
+...
+40 |   impl<T: Unpin, U: Unpin> Unpin for Baz<T, U> {} // Conditional Unpin impl
+   |   -------------------------------------------- first implementation here
+   |
+   = note: this error originates in the macro `$crate::__pin_project_make_unpin_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `Unpin` for type `Qux<_, _>`
+  --> tests/ui/pin_project/conflict-unpin.rs:42:1
+   |
+42 | / pin_project! { //~ ERROR E0119
+43 | |     #[project(!Unpin)]
+44 | |     struct Qux<T, U> {
+45 | |         #[pin]
+...  |
+49 | | }
+   | |_^ conflicting implementation for `Qux<_, _>`
+...
+52 |   impl<T, U> Unpin for Qux<T, U> {} // Non-conditional Unpin impl
+   |   ------------------------------ first implementation here
+   |
+   = note: upstream crates may add a new impl of trait `std::marker::Unpin` for type `(std::marker::PhantomData<&()>, std::marker::PhantomPinned)` in future versions
+   = note: this error originates in the macro `$crate::__pin_project_make_unpin_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `Unpin` for type `Fred<_, _>`
+  --> tests/ui/pin_project/conflict-unpin.rs:54:1
+   |
+54 | / pin_project! { //~ ERROR E0119
+55 | |     #[project(!Unpin)]
+56 | |     struct Fred<T, U> {
+57 | |         #[pin]
+...  |
+61 | | }
+   | |_^ conflicting implementation for `Fred<_, _>`
+...
+64 |   impl<T: Unpin, U: Unpin> Unpin for Fred<T, U> {} // Conditional Unpin impl
+   |   --------------------------------------------- first implementation here
+   |
+   = note: upstream crates may add a new impl of trait `std::marker::Unpin` for type `(std::marker::PhantomData<&()>, std::marker::PhantomPinned)` in future versions
+   = note: this error originates in the macro `$crate::__pin_project_make_unpin_impl` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)