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/src/tests/contains.rs

@@ -0,0 +1,108 @@
+use super::*;
+
+use crate::Flags;
+
+#[test]
+fn cases() {
+    case(
+        TestFlags::empty(),
+        &[
+            (TestFlags::empty(), true),
+            (TestFlags::A, false),
+            (TestFlags::B, false),
+            (TestFlags::C, false),
+            (TestFlags::from_bits_retain(1 << 3), false),
+        ],
+        TestFlags::contains,
+    );
+
+    case(
+        TestFlags::A,
+        &[
+            (TestFlags::empty(), true),
+            (TestFlags::A, true),
+            (TestFlags::B, false),
+            (TestFlags::C, false),
+            (TestFlags::ABC, false),
+            (TestFlags::from_bits_retain(1 << 3), false),
+            (TestFlags::from_bits_retain(1 | (1 << 3)), false),
+        ],
+        TestFlags::contains,
+    );
+
+    case(
+        TestFlags::ABC,
+        &[
+            (TestFlags::empty(), true),
+            (TestFlags::A, true),
+            (TestFlags::B, true),
+            (TestFlags::C, true),
+            (TestFlags::ABC, true),
+            (TestFlags::from_bits_retain(1 << 3), false),
+        ],
+        TestFlags::contains,
+    );
+
+    case(
+        TestFlags::from_bits_retain(1 << 3),
+        &[
+            (TestFlags::empty(), true),
+            (TestFlags::A, false),
+            (TestFlags::B, false),
+            (TestFlags::C, false),
+            (TestFlags::from_bits_retain(1 << 3), true),
+        ],
+        TestFlags::contains,
+    );
+
+    case(
+        TestZero::ZERO,
+        &[(TestZero::ZERO, true)],
+        TestZero::contains,
+    );
+
+    case(
+        TestOverlapping::AB,
+        &[
+            (TestOverlapping::AB, true),
+            (TestOverlapping::BC, false),
+            (TestOverlapping::from_bits_retain(1 << 1), true),
+        ],
+        TestOverlapping::contains,
+    );
+
+    case(
+        TestExternal::all(),
+        &[
+            (TestExternal::A, true),
+            (TestExternal::B, true),
+            (TestExternal::C, true),
+            (TestExternal::from_bits_retain(1 << 5 | 1 << 7), true),
+        ],
+        TestExternal::contains,
+    );
+}
+
+#[track_caller]
+fn case<T: Flags + std::fmt::Debug + Copy>(
+    value: T,
+    inputs: &[(T, bool)],
+    mut inherent: impl FnMut(&T, T) -> bool,
+) {
+    for (input, expected) in inputs {
+        assert_eq!(
+            *expected,
+            inherent(&value, *input),
+            "{:?}.contains({:?})",
+            value,
+            input
+        );
+        assert_eq!(
+            *expected,
+            Flags::contains(&value, *input),
+            "Flags::contains({:?}, {:?})",
+            value,
+            input
+        );
+    }
+}