fix: restore registry-based Docker layer caching in CI

Replace --no-cache with --cache-from/--cache-to registry caching,
matching the cameleer3-server CI pattern. The ephemeral CI runner
destroys BuildKit local cache after each job, so only registry
caching persists between runs.

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

.gitea/workflows/ci.yml

@@ -102,7 +102,8 @@ jobs:
           docker buildx build --platform linux/amd64 \
             --build-arg REGISTRY_TOKEN="$REGISTRY_TOKEN" \
             $TAGS \
-            --no-cache \
+            --cache-from type=registry,ref=gitea.siegeln.net/cameleer/cameleer-saas:buildcache \
+            --cache-to type=registry,ref=gitea.siegeln.net/cameleer/cameleer-saas:buildcache,mode=max \
             --provenance=false \
             --push .
         env:
@@ -118,7 +119,8 @@ jobs:
             --build-arg REGISTRY_TOKEN="$REGISTRY_TOKEN" \
             -f ui/sign-in/Dockerfile \
             $TAGS \
-            --no-cache \
+            --cache-from type=registry,ref=gitea.siegeln.net/cameleer/cameleer-logto:buildcache \
+            --cache-to type=registry,ref=gitea.siegeln.net/cameleer/cameleer-logto:buildcache,mode=max \
             --provenance=false \
             --push ui/sign-in/
         env: