fix(ci): iOS Flutter download adds GitHub mirror fallback

The macOS runner cannot reach Google Cloud storage. Add a fallback
to the GitHub Flutter releases mirror with a 10s connect timeout
so the build doesn't hang indefinitely.

.gitea/workflows/ci.yml

@@ -237,8 +237,13 @@ jobs:
       - name: Setup Flutter
         run: |
           set -e
-          curl -fsSL "https://storage.googleapis.com/flutter_infra_release/releases/stable/macos/flutter_macos_${{ env.FLUTTER_VERSION }}-stable.tar.xz" \
+          # Try Google storage, fallback to GitHub mirror
+          if ! curl -fsSL --connect-timeout 10 "https://storage.googleapis.com/flutter_infra_release/releases/stable/macos/flutter_macos_${{ env.FLUTTER_VERSION }}-stable.tar.xz" \
+              -o /tmp/flutter.tar.xz 2>/dev/null; then
+            echo "Google storage unavailable, trying GitHub mirror..."
+            curl -fsSL "https://github.com/flutter/flutter/releases/download/${{ env.FLUTTER_VERSION }}-stable/flutter_macos_${{ env.FLUTTER_VERSION }}-stable.tar.xz" \
               -o /tmp/flutter.tar.xz
+          fi
           tar -xf /tmp/flutter.tar.xz -C "$PWD"
           export PATH="$PWD/flutter/bin:$PATH"
           flutter --version