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/packed.stderr

@@ -0,0 +1,95 @@
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:5:1
+   |
+ 5 | / pin_project! { //~ ERROR reference to packed field is unaligned
+ 6 | |     #[repr(packed, C)]
+ 7 | |     struct Packed {
+ 8 | |         #[pin]
+...  |
+11 | | }
+   | |_^
+   |
+   = note: this struct is 1-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_struct_make_proj_method` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:5:1
+   |
+ 5 | / pin_project! { //~ ERROR reference to packed field is unaligned
+ 6 | |     #[repr(packed, C)]
+ 7 | |     struct Packed {
+ 8 | |         #[pin]
+...  |
+11 | | }
+   | |_^
+   |
+   = note: this struct is 1-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_struct_make_proj_method` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:5:1
+   |
+ 5 | / pin_project! { //~ ERROR reference to packed field is unaligned
+ 6 | |     #[repr(packed, C)]
+ 7 | |     struct Packed {
+ 8 | |         #[pin]
+...  |
+11 | | }
+   | |_^
+   |
+   = note: this struct is 1-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_constant` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:13:1
+   |
+13 | / pin_project! { //~ ERROR reference to packed field is unaligned
+14 | |     #[repr(packed(2))]
+15 | |     struct PackedN {
+16 | |         #[pin]
+...  |
+19 | | }
+   | |_^
+   |
+   = note: this struct is at most 2-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_struct_make_proj_method` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:13:1
+   |
+13 | / pin_project! { //~ ERROR reference to packed field is unaligned
+14 | |     #[repr(packed(2))]
+15 | |     struct PackedN {
+16 | |         #[pin]
+...  |
+19 | | }
+   | |_^
+   |
+   = note: this struct is at most 2-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_struct_make_proj_method` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0793]: reference to field of packed struct is unaligned
+  --> tests/ui/pin_project/packed.rs:13:1
+   |
+13 | / pin_project! { //~ ERROR reference to packed field is unaligned
+14 | |     #[repr(packed(2))]
+15 | |     struct PackedN {
+16 | |         #[pin]
+...  |
+19 | | }
+   | |_^
+   |
+   = note: this struct is at most 2-byte aligned, but the type of this field may require higher alignment
+   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::__pin_project_constant` which comes from the expansion of the macro `pin_project` (in Nightly builds, run with -Z macro-backtrace for more info)