ci(android): fix CI runner (JDK/SDK/gradlew) + variant test

PR #2 merged the M0 scaffold with the initial CI, which fails on this
self-hosted runner. Fix forward:

- JDK 17 via apt (openjdk-17-jdk-headless) + JAVA_HOME, replacing
  actions/setup-java: the runner can't resolve api.adoptium.net (EAI_AGAIN).
- Explicit `sdkmanager` install of platform-tools + platforms;android-35 +
  build-tools;35.0.0 so the build never relies on AGP auto-download.
- `chmod +x ./gradlew` in the run step (and set the 100755 git bit): this
  runner's checkout drops file modes, so `./gradlew` alone hit
  "Permission denied" (exit 126).
- ScaffoldSanityTest: drop the BuildConfig.DEBUG assertion, which fails under
  testReleaseUnitTest (the `test` task runs both variants); assert VERSION_NAME.
- Remove the redundant android:label on MainActivity (RedundantLabel lint).

Verified locally against the Android Studio SDK (platform 35 + build-tools
35.0.0): `./gradlew lint test assembleDebug` passes and builds a debug APK.

Co-Authored-By: Claude <noreply@anthropic.com>

.gitea/workflows/pr-checks.yml

@@ -8,10 +8,13 @@
 #     * Enable Status Check
 #     * Status check patterns:  PR Checks / *
 #
-# Runner: the org's self-hosted `ubuntu-latest`, on a bare `ubuntu:latest`
-# container that lacks git/curl/unzip (needed by checkout + sdkmanager) -- so the
-# first step installs them. (Faster later: switch to a prebuilt Android-SDK
-# container image so nothing installs per-run.)
+# Runner: the org's self-hosted `ubuntu-latest`. The container lacks
+# git/curl/unzip (needed by checkout + sdkmanager), so the first step installs
+# them. It also installs JDK 17 from the Ubuntu archive rather than using
+# actions/setup-java, because this runner can't resolve api.adoptium.net (that
+# download fails with EAI_AGAIN) while the Ubuntu mirrors are reachable.
+# (Faster later: switch to a prebuilt Android-SDK+JDK container image so nothing
+# installs per-run.)
 
 name: PR Checks
 
@@ -27,23 +30,24 @@ jobs:
   android-build:
     runs-on: ubuntu-latest
     steps:
-      # Bare ubuntu:latest is missing the tools checkout + the SDK installer need.
-      - name: Install base tools
+      # Install the tools checkout + the SDK installer need, plus JDK 17 (see the
+      # header note on why we avoid actions/setup-java on this runner).
+      - name: Install base tools + JDK 17
         run: |
           apt-get update
-          apt-get install -y git curl unzip
+          apt-get install -y git curl unzip openjdk-17-jdk-headless
+          echo "JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64" >> "$GITHUB_ENV"
 
       - uses: actions/checkout@v4
 
-      - name: Set up JDK 17
-        uses: actions/setup-java@v4
-        with:
-          distribution: temurin
-          java-version: "17"
-
       - name: Set up Android SDK
         uses: android-actions/setup-android@v3
 
+      # Install exactly what the build targets so it never depends on AGP's
+      # build-time auto-download. `yes |` accepts any license prompts.
+      - name: Install Android SDK packages
+        run: yes | sdkmanager "platform-tools" "platforms;android-35" "build-tools;35.0.0"
+
       - name: Cache Gradle
         uses: actions/cache@v4
         with:
@@ -54,5 +58,9 @@ jobs:
           restore-keys: |
             gradle-${{ runner.os }}-
 
+      # chmod defensively: this runner's checkout doesn't preserve the git
+      # executable bit, so `./gradlew` alone fails with "Permission denied".
       - name: Lint, test, assemble debug
-        run: ./gradlew --no-daemon lint test assembleDebug
+        run: |
+          chmod +x ./gradlew
+          ./gradlew --no-daemon lint test assembleDebug