perf(ci): optimize Android build with reduced targets and Rust cache

- Cache Rust target directories for Android (aarch64, armv7)
- Remove i686 and x86_64 targets (emulator-only, rarely needed)
- Expected to reduce build time from ~8min to under 5min

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: pythoninthegrass

.github/actions/setup-tauri-build/action.yml

@@ -66,7 +66,7 @@ runs:
       if: inputs.platform == 'android'
       uses: dtolnay/rust-toolchain@stable
       with:
-        targets: aarch64-linux-android,armv7-linux-androideabi,i686-linux-android,x86_64-linux-android
+        targets: aarch64-linux-android,armv7-linux-androideabi
 
     - name: Cache Task checksums
       uses: actions/cache@v5
@@ -91,7 +91,10 @@ runs:
       id: cache-build-android
       uses: actions/cache@v5
       with:
-        path: src-tauri/gen/android/app/build
+        path: |
+          src-tauri/gen/android/app/build
+          src-tauri/target/aarch64-linux-android
+          src-tauri/target/armv7-linux-androideabi
         key: ${{ runner.os }}-android-build-${{ hashFiles('src-tauri/src/**/*.rs', 'src-tauri/Cargo.toml', 'src-tauri/Cargo.lock', 'src-tauri/tauri.conf.json', 'src-tauri/dist/**/*', 'src-tauri/icons/icon.png', 'fastlane/Fastfile', 'fastlane/Appfile') }}
         restore-keys: |
           ${{ runner.os }}-android-build-