fix: use mode=min for Docker build cache to avoid Hub blob limits

mode=max pushes all intermediate layers to Docker Hub as cache, which
exceeds blob size limits when the base image changes. mode=min only
caches final image layers — smaller push, still provides cache hits
for the most common rebuild scenario (code changes, same base).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -56,7 +56,7 @@ jobs:
           push: true
           tags: ${{ steps.tags.outputs.tags }}
           cache-from: type=registry,ref=manticorum67/paper-dynasty-database:buildcache
-          cache-to: type=registry,ref=manticorum67/paper-dynasty-database:buildcache,mode=max
+          cache-to: type=registry,ref=manticorum67/paper-dynasty-database:buildcache,mode=min
 
       - name: Tag release
         if: success() && github.ref == 'refs/heads/main'