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/unicase/.github/workflows/CI.yml

@@ -0,0 +1,83 @@
+name: CI
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+env:
+  RUST_BACKTRACE: 1
+
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
+jobs:
+  ci-pass:
+    name: CI is green
+    runs-on: ubuntu-latest
+    needs:
+      - style
+      - test
+      - msrv
+    steps:
+      - run: exit 0
+
+  style:
+    name: Check Style
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+
+      - name: cargo fmt --check
+        run: cargo fmt --check
+
+  test:
+    name: Test ${{ matrix.rust }} on ${{ matrix.os }}
+    needs: [style]
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - beta
+
+        os:
+          - ubuntu-latest
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Rust (${{ matrix.rust }})
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+
+      - name: Test
+        run: cargo test
+
+  msrv:
+    name: Check MSRV
+    needs: [style]
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Rust MSRV
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: 1.36.0
+
+      - name: Check
+        run: cargo build
+