ci: Switch to CalVer (YYYY.MM.BUILD) with auto-generated versions

Remove manual semver validation from PR checks. Versions are now
auto-generated on merge to main by counting existing monthly tags.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/docker-build.yml

@@ -30,7 +30,6 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Login to Docker Hub
-        if: github.ref == 'refs/heads/main'
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
@@ -61,11 +60,26 @@ jobs:
 
           echo "CalVer version: ${VERSION}"
 
-      - name: Build Docker image
+      # Dev build: push with dev + dev-SHA tags (PR/feature branches)
+      - name: Build Docker image (dev)
+        if: github.ref != 'refs/heads/main'
         uses: docker/build-push-action@v5
         with:
           context: .
-          push: ${{ github.ref == 'refs/heads/main' }}
+          push: true
+          tags: |
+            manticorum67/paper-dynasty-discordapp:dev
+            manticorum67/paper-dynasty-discordapp:dev-${{ steps.meta.outputs.sha_short }}
+          cache-from: type=registry,ref=manticorum67/paper-dynasty-discordapp:buildcache
+          cache-to: type=registry,ref=manticorum67/paper-dynasty-discordapp:buildcache,mode=max
+
+      # Production build: push with latest + CalVer tags (main only)
+      - name: Build Docker image (production)
+        if: github.ref == 'refs/heads/main'
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
           tags: |
             manticorum67/paper-dynasty-discordapp:latest
             manticorum67/paper-dynasty-discordapp:${{ steps.meta.outputs.version }}