ci: drop non-functional cache steps (act_runner cache server unreachable)

The internal cache server times out (reserveCache/getCacheEntry Request
timeout), so caching never hit and the Post Cache step hung ~2 min
tarring the SDK for nothing. Install the SDK fresh each run instead —
slower but reliable and no post-step hang.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -23,15 +23,7 @@ jobs:
           distribution: temurin
           java-version: '17'
 
-      - name: Cache Android SDK
-        id: sdk-cache
-        uses: actions/cache@v3
-        with:
-          path: ${{ github.workspace }}/android-sdk
-          key: android-sdk-cmdline9862592-platform34-buildtools3400
-
       - name: Install Android SDK
-        if: steps.sdk-cache.outputs.cache-hit != 'true'
         run: |
           set -e
           SDK="$GITHUB_WORKSPACE/android-sdk"
@@ -49,14 +41,6 @@ jobs:
       - name: Point Gradle at the SDK
         run: echo "sdk.dir=$GITHUB_WORKSPACE/android-sdk" > local.properties
 
-      - name: Cache Gradle
-        uses: actions/cache@v3
-        with:
-          path: |
-            ~/.gradle/caches
-            ~/.gradle/wrapper
-          key: gradle-${{ hashFiles('**/*.gradle*', 'gradle/wrapper/gradle-wrapper.properties') }}
-
       # ── Debug build: every push/PR that is NOT a tag ───────────────────────
       - name: Build debug APK
         if: ${{ !startsWith(github.ref, 'refs/tags/') }}