fix(ci): install Android SDK command-line tools on ubuntu-latest runner

The Gitea Actions ubuntu-latest image does not include the Android SDK
(unlike GitHub Actions). Add an explicit step to download cmdline-tools,
install platform-tools, platforms;android-35, and build-tools;35.0.0,
then export ANDROID_HOME and PATH via GITEA_ENV_FILE/GITEA_PATH_FILE
so subsequent flutter precache and flutter build apk steps can find it.

.gitea/workflows/ci.yml

@@ -106,6 +106,20 @@ jobs:
           flutter-version: ${{ env.FLUTTER_VERSION }}
           cache: true
 
+      - name: Install Android SDK command-line tools
+        run: |
+          export ANDROID_HOME="${HOME}/android-sdk"
+          mkdir -p "${ANDROID_HOME}/cmdline-tools"
+          curl -fsSL "https://dl.google.com/android/repository/commandlinetools-linux-11076708_latest.zip" -o cmdline-tools.zip
+          unzip -q cmdline-tools.zip -d "${ANDROID_HOME}/cmdline-tools"
+          mv "${ANDROID_HOME}/cmdline-tools/cmdline-tools" "${ANDROID_HOME}/cmdline-tools/latest"
+          export PATH="${ANDROID_HOME}/cmdline-tools/latest/bin:${PATH}"
+          yes | sdkmanager --licenses >/dev/null 2>&1 || true
+          sdkmanager "platform-tools" "platforms;android-35" "build-tools;35.0.0"
+          echo "ANDROID_HOME=${ANDROID_HOME}" >> "${GITEA_ENV_FILE}"
+          echo "${ANDROID_HOME}/cmdline-tools/latest/bin" >> "${GITEA_PATH_FILE}"
+          echo "${ANDROID_HOME}/platform-tools" >> "${GITEA_PATH_FILE}"
+
       - name: Pre-cache Android platform artifacts
         run: flutter precache --android