Simplify Forgejo Actions workflow for compatibility

- Remove GitHub Actions marketplace actions (uses directive)
- Use shell commands instead for better compatibility
- Switch from gitea context to github context variables
- Use Docker container to run build commands

Fixes YAML schema validation errors in Forgejo runner

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

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

.forgejo/workflows/docker-build.yml

@@ -4,54 +4,30 @@ on:
   push:
     branches:
       - main
-  pull_request:
-    branches:
-      - main
-
-env:
-  REGISTRY: forgejo.sivic.me
-  IMAGE_NAME: ${{ gitea.repository }}
 
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
+    container:
+      image: docker:latest
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        run: |
+          apk add --no-cache git
+          git clone ${{ github.server_url }}/${{ github.repository }} .
+          git checkout ${{ github.sha }}
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+      - name: Build Docker image
+        run: |
+          docker build -t forgejo.sivic.me/${{ github.repository }}:latest \
+                       -t forgejo.sivic.me/${{ github.repository }}:${{ github.sha }} .
 
       - name: Log in to Forgejo Container Registry
-        uses: docker/login-action@v3
-        with:
-          registry: ${{ env.REGISTRY }}
-          username: ${{ gitea.actor }}
-          password: ${{ secrets.GITEA_TOKEN }}
+        run: |
+          echo "${{ secrets.GITEA_TOKEN }}" | docker login forgejo.sivic.me -u ${{ github.actor }} --password-stdin
 
-      - name: Extract metadata for Docker
-        id: meta
-        uses: docker/metadata-action@v5
-        with:
-          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-          tags: |
-            type=ref,event=branch
-            type=ref,event=pr
-            type=semver,pattern={{version}}
-            type=semver,pattern={{major}}.{{minor}}
-            type=sha,prefix={{branch}}-
-            type=raw,value=latest,enable={{is_default_branch}}
-
-      - name: Build and push Docker image
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          push: ${{ github.event_name != 'pull_request' }}
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-          cache-from: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache
-          cache-to: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache,mode=max
+      - name: Push Docker image
+        run: |
+          docker push forgejo.sivic.me/${{ github.repository }}:latest
+          docker push forgejo.sivic.me/${{ github.repository }}:${{ github.sha }}