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/memo-map/.github/workflows/clippy.yml

@@ -0,0 +1,18 @@
+name: Clippy
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          components: clippy, rustfmt
+          override: true
+      - name: Run clippy
+        run: make lint

vendor/memo-map/.github/workflows/rustfmt.yml

@@ -0,0 +1,18 @@
+name: Rustfmt
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          components: clippy, rustfmt
+          override: true
+      - name: Run rustfmt
+        run: make format-check

vendor/memo-map/.github/workflows/tests.yml

@@ -0,0 +1,47 @@
+name: Tests
+
+on: [push]
+
+jobs:
+  build-latest:
+    name: Test on Latest
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          override: true
+      - name: Test
+        run: make test
+
+  build-stable:
+    name: Build on 1.43.0
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.43.0
+          profile: minimal
+          override: true
+      - name: Test
+        run: cargo check --all-features
+
+  miri-test-latest:
+    name: Miri Test
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          profile: minimal
+          components: miri
+          override: true
+      - name: Miri Test
+        run: make miri-test