feat(ci): cache iOS build artifacts for full skip optimization

Cache src-tauri/gen/apple/build with source-hash key so Task
fingerprinting can skip entire build when IPA exists and
sources unchanged.

Author: pythoninthegrass

.github/workflows/build-ios-app.yml

@@ -75,6 +75,14 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-task-
 
+      - name: Cache iOS build artifacts
+        uses: actions/cache@v5
+        with:
+          path: src-tauri/gen/apple/build
+          key: ${{ runner.os }}-ios-build-${{ 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 }}-ios-build-
+
       - name: Install Task
         uses: go-task/setup-task@v1