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/bitflags-1.3.2/tests/compile-fail/impls/copy.rs

@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(Clone, Copy)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}

vendor/bitflags-1.3.2/tests/compile-fail/impls/copy.stderr.beta

@@ -0,0 +1,27 @@
+error[E0119]: conflicting implementations of trait `std::clone::Clone` for type `Flags`
+ --> $DIR/copy.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(Clone, Copy)]
+  | |              ----- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::Copy` for type `Flags`
+ --> $DIR/copy.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(Clone, Copy)]
+  | |                     ---- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)

vendor/bitflags-1.3.2/tests/compile-fail/impls/eq.rs

@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(PartialEq, Eq)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}

vendor/bitflags-1.3.2/tests/compile-fail/impls/eq.stderr.beta

@@ -0,0 +1,55 @@
+error[E0119]: conflicting implementations of trait `std::cmp::PartialEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |              --------- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::cmp::Eq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |                         -- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::StructuralPartialEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |              --------- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::StructuralEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |                         -- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)