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/version_check/.github/workflows/ci.yml

@@ -0,0 +1,42 @@
+name: CI
+
+on: [push, pull_request]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  test:
+    name: "${{ matrix.os.name }} ${{ matrix.test.name }} (${{ matrix.toolchain }})"
+
+    strategy:
+      matrix:
+        os:
+          - { name: Linux, distro: ubuntu-latest }
+          - { name: Windows, distro: windows-latest }
+          - { name: macOS, distro: macOS-latest }
+        toolchain: [nightly, beta, stable]
+        include:
+          - os: { name: Linux, distro: ubuntu-latest }
+            toolchain: 1.0.0
+
+    runs-on: ${{ matrix.os.distro }}
+
+    steps:
+      - name: Checkout Sources
+        uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.toolchain }}
+          override: true
+
+      - name: Run Tests
+        uses: actions-rs/cargo@v1
+        env:
+          FORCE_STATIC: 1
+          KNOWN_CHANNEL: ${{ matrix.toolchain }}
+        with:
+          command: test