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/usb-device/.github/workflows/ci.yml

@@ -0,0 +1,35 @@
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+name: CI
+
+jobs:
+  ci-linux:
+    name: CI
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        rust: [stable]
+
+        include:
+          # Test nightly but don't fail
+          - rust: nightly
+            experimental: true
+            TARGET: x86_64-unknown-linux-gnu
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+          targets: ${{ matrix.TARGET }}
+
+      - name: Install libusb library
+        run: sudo apt-get install -y libusb-1.0.0-dev
+
+      - run: cargo check --all-targets
+      - run: cargo check --features control-buffer-256
+      - run: cargo check --features defmt

vendor/usb-device/.github/workflows/rustfmt.yml

@@ -0,0 +1,21 @@
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+name: Code formatting check
+
+jobs:
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - run: cargo fmt --all -- --check
+      - run: cargo clippy --all-features
+      - run: cargo clippy --features defmt
+      - run: cargo clippy --features control-buffer-256
+      - run: cargo clippy