revert(ci): remove docker-build, acknowledge Forgejo limitations

After extensive testing, confirmed that Docker builds are not possible
in Forgejo CI due to network isolation:

Tested approaches:
❌ Socket mount (/var/run/docker.sock)
❌ DinD service with TCP
❌ Buildx with various configs
❌ Direct host Docker access
❌ runs-on:docker without container

Root cause: Forgejo act runner creates isolated networks for each job.
No way to access Docker daemon from within these networks.

Solution: Handle Docker builds separately via deployment scripts.
This is a pragmatic solution that works within Forgejo's infrastructure.

CI focuses on what it can do well: code quality checks.

.forgejo/workflows/lint-and-build.yml

@@ -1,4 +1,4 @@
-name: Lint, Build, and Docker
+name: Lint and Build
 
 on:
   push:
@@ -95,45 +95,19 @@ jobs:
         run: cargo build --release --verbose
 
   # ==============================================================================
-  # Job 4: Docker Build - Try accessing host Docker via DOCKER_HOST
+  # NOTE: Docker builds are handled separately due to Forgejo runner limitations
+  # 
+  # The Forgejo act runner creates isolated networks for each job, making it
+  # impossible to access Docker from within CI jobs. All attempts to work around
+  # this have failed:
+  # - Socket mount: Socket not accessible in container
+  # - DinD service: DNS resolution fails across networks  
+  # - Buildx: Same network isolation issues
+  # - Direct host access: Network isolation prevents this
+  # 
+  # Docker builds are done separately:
+  # - Locally: docker build -f backend/docker/Dockerfile
+  # - On Solaria: docs/deployment/deploy-to-solaria.sh
+  # 
+  # This is a pragmatic solution that works within Forgejo's infrastructure.
   # ==============================================================================
-  docker-build:
-    runs-on: docker
-    needs: [build]
-    
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@v4
-      
-      - name: Try accessing Docker
-        run: |
-          echo "Checking Docker availability..."
-          # Try various Docker host options
-          if docker info >/dev/null 2>&1; then
-            echo "✅ Docker accessible via default socket"
-          elif docker -H unix:///var/run/docker.sock info >/dev/null 2>&1; then
-            echo "✅ Docker accessible via /var/run/docker.sock"
-            export DOCKER_HOST=unix:///var/run/docker.sock
-          elif docker -H tcp://127.0.0.1:2375 info >/dev/null 2>&1; then
-            echo "✅ Docker accessible via TCP localhost"
-            export DOCKER_HOST=tcp://127.0.0.1:2375
-          elif docker -H tcp://172.17.0.1:2375 info >/dev/null 2>&1; then
-            echo "✅ Docker accessible via Docker bridge"
-            export DOCKER_HOST=tcp://172.17.0.1:2375
-          else
-            echo "❌ Docker not accessible"
-            echo "Available network interfaces:"
-            ip addr show
-            exit 1
-          fi
-      
-      - name: Show Docker version
-        run: docker version
-      
-      - name: Build Docker image
-        working-directory: ./backend
-        run: |
-          docker build -f docker/Dockerfile -t normogen-backend:${{ github.sha }} -t normogen-backend:latest .
-      
-      - name: Show images
-        run: docker images normogen-backend