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/static_cell/.github/workflows/clippy.yml

@@ -0,0 +1,25 @@
+name: Clippy check
+
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+jobs:
+  clippy:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - rust: 1.56
+          - rust: 1.63
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{matrix.rust}}
+            components: clippy
+            override: true
+      - name: Clippy check
+        run: cargo clippy

vendor/static_cell/.github/workflows/rustfmt.yml

@@ -0,0 +1,14 @@
+name: Code formatting check
+
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+jobs:
+  rustfmt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Check fmt
+        run: cargo fmt -- --check

vendor/static_cell/.github/workflows/test.yml

@@ -0,0 +1,36 @@
+name: Test
+
+on:
+  push:
+    branches: [ staging, trying, master ]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - rust: 1.56
+          - rust: 1.63
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{matrix.rust}}
+            components: clippy
+            override: true
+      - name: Test
+        run: cargo test
+  test-nightly:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: nightly
+            override: true
+      - name: Test
+        run: cargo test --features nightly