Fix Hugo extended build dependencies

- Add gcc, g++, musl-dev for C compilation
- Add libwebp-dev and libsass-dev for Hugo extended features
- Resolves build constraint errors for WebP and SASS support

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.gitea/workflows/build_hugo.yaml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: docker
     steps:
-      - run: apk add --no-cache nodejs rsync
+      - run: apk add --no-cache nodejs rsync gcc g++ musl-dev libwebp-dev libsass-dev
       - uses: actions/checkout@v4
         with:
           submodules: 'true'