feat: add offline wake-word detection with sherpa-onnx

- Integrate sherpa-onnx for local "Computer" wake-word detection
- Add foreground service (microphone type) for continued listening across apps
- Request RECORD_AUDIO, POST_NOTIFICATIONS, and foreground service permissions
- Download and verify pinned sherpa-onnx model (17 MB) on first enable
- Update LauncherViewModel with wake-word state and controller
- Add WorkManager and commons-compress dependencies for model extraction
- Update README with wake-word feature details and limitations

.github/workflows/android-apk.yml

@@ -0,0 +1,51 @@
+name: Build Android APK
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+      - master
+  pull_request:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: android-apk-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-debug-apk:
+    name: Build debug APK
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v6
+
+      - name: Set up Java 17
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: "17"
+
+      # This repository does not currently contain Gradle wrapper files.
+      # AGP 8.7.x requires Gradle 8.9.
+      - name: Set up Gradle 8.9
+        uses: gradle/actions/setup-gradle@v6
+        with:
+          gradle-version: "8.9"
+          cache-provider: basic
+
+      - name: Build installable debug APK
+        run: gradle :app:assembleDebug --no-daemon --stacktrace
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v6
+        with:
+          name: ambient-launcher-debug-${{ github.run_number }}
+          path: app/build/outputs/apk/debug/*.apk
+          if-no-files-found: error
+          retention-days: 14