prebuilt: initial Lawnchair prebuilt setup and build infrastructure

Initial Lawnchair prebuilt APK integration for PawletOS:
- Add priv-app/Lawnchair install target with Android.bp
- Add QuickstepSwitcherOverlay to override AOSP launcher
- Wire lawnchair.mk into product makefiles
- Add build_prebuilt.sh for Gradle -> prebuilt APK workflow
- Iteratively update from Lawnchair 2.1-alpha through 12 Alpha 5,
  12.1 Alpha 3, and 15 Beta 1 as upstream releases landed

build_prebuilt.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# Build a Lawnchair APK from source and place it here as a prebuilt.
+#
+# Usage:
+#   ./build_prebuilt.sh [path/to/apps_lawnchair]
+#
+# If no path is given, looks for apps_lawnchair as a sibling directory.
+# After running this, the APK still needs to be platform-signed before it
+# works as a privileged system app in a ROM build:
+#
+#   apksigner sign \
+#     --key   $ANDROID_BUILD_TOP/build/target/product/security/platform.pk8 \
+#     --cert  $ANDROID_BUILD_TOP/build/target/product/security/platform.x509.pem \
+#     priv-app/Lawnchair/Lawnchair.apk
+#
+# If you're only testing on a rooted device you can push the unsigned APK
+# directly and use pm to set it as the default launcher.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+SRC_DIR="${1:-$(dirname "$SCRIPT_DIR")/Lawnchair}"
+
+if [[ ! -f "$SRC_DIR/gradlew" ]]; then
+    echo "ERROR: Lawnchair source not found at: $SRC_DIR"
+    echo "Pass the path as the first argument: $0 /path/to/apps_lawnchair"
+    exit 1
+fi
+
+echo "==> Building Lawnchair from $SRC_DIR"
+cd "$SRC_DIR"
+./gradlew assembleLawnchairRelease --stacktrace
+
+APK=$(find . -name "*.apk" -path "*/lawnchair/release/*" | grep -v unsigned | head -1)
+if [[ -z "$APK" ]]; then
+    # Fallback: any release APK
+    APK=$(find . -name "*.apk" -path "*/release/*" | head -1)
+fi
+if [[ -z "$APK" ]]; then
+    echo "ERROR: No release APK found after Gradle build."
+    exit 1
+fi
+
+DEST="$SCRIPT_DIR/priv-app/Lawnchair/Lawnchair.apk"
+cp "$APK" "$DEST"
+echo ""
+echo "==> APK copied to: $DEST"
+echo ""
+echo "Next steps for AOSP ROM integration:"
+echo "  1. Sign with the platform key (see header comment in this script)"
+echo "  2. Commit the signed APK:  git -C '$SCRIPT_DIR' add priv-app/Lawnchair/Lawnchair.apk && git commit"
+echo "  3. Switch the manifest to prebuilt mode (see android_local_manifest/pawletos.xml)"
+echo ""
+echo "For direct device testing (root required):"
+echo "  adb push $DEST /system/priv-app/Lawnchair/Lawnchair.apk"
+echo "  adb shell am force-stop app.lawnchair"
+echo "  adb reboot"

priv-app/Lawnchair/Android.bp

@@ -16,4 +16,25 @@ android_app_import {
         "androidx.window.extensions",
         "androidx.window.sidecar",
     ],
-}
+}
+
+// Include this alongside Lawnchair to also replace the QuickStep/recents
+// launcher (Launcher3QuickStep). Both modules reference the same APK;
+// the package manager deduplicates at install time.
+android_app_import {
+    name: "LawnchairQuickStep",
+    apk: "Lawnchair.apk",
+    privileged: true,
+    certificate: "platform",
+    overrides: [
+        "Launcher3QuickStep",
+    ],
+    required: [
+        "privapp-permissions-app.lawnchair.xml",
+        "app.lawnchair-hiddenapi-package-whitelist.xml",
+    ],
+    optional_uses_libs: [
+        "androidx.window.extensions",
+        "androidx.window.sidecar",
+    ],
+}