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/micromath/.github/workflows/CI.yml

@@ -0,0 +1,100 @@
+name: CI
+
+on:
+  pull_request: {}
+  push:
+    branches: main
+
+env:
+  CARGO_INCREMENTAL: 0
+  RUSTFLAGS: "-Dwarnings"
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          profile: minimal
+      - run: cargo check
+
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - 1.47.0 # MSRV
+          - stable
+        target:
+          # - armv7a-none-eabi
+          - thumbv7em-none-eabi
+          - wasm32-unknown-unknown
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+          override: true
+          profile: minimal
+      - run: cargo build --target ${{ matrix.target }} --release --no-default-features
+      - run: cargo build --target ${{ matrix.target }} --release --no-default-features --features num-traits
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          # 32-bit Linux
+          - target: i686-unknown-linux-gnu
+            rust: 1.47.0 # MSRV
+            deps: sudo apt update && sudo apt install gcc-multilib
+          - target: i686-unknown-linux-gnu
+            rust: stable
+            deps: sudo apt update && sudo apt install gcc-multilib
+
+          # 64-bit Linux
+          - target: x86_64-unknown-linux-gnu
+            rust: 1.47.0 # MSRV
+          - target: x86_64-unknown-linux-gnu
+            rust: stable
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+          override: true
+          profile: minimal
+      - run: ${{ matrix.deps }}
+      - run: cargo test --target ${{ matrix.target }} --release --all-features
+
+  rustfmt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          components: rustfmt
+          override: true
+          profile: minimal
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+  clippy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.47.0 # MSRV
+          components: clippy
+          override: true
+          profile: minimal
+      - run: cargo clippy -- -D warnings