Improve main branch workflow: add path filter + registry layer caching for faster builds

.gitea/workflows/build-main.yml

@@ -4,6 +4,11 @@ on:
   push:
     branches:
       - main
+    paths:
+      - '**.py'
+      - 'requirements.txt'
+      - 'Dockerfile'
+      - '.gitea/workflows/**'
 
 jobs:
   build:
@@ -26,7 +31,7 @@ jobs:
         id: vars
         run: echo "SHORT_SHA=$(git rev-parse --short HEAD)" >> $GITHUB_OUTPUT
 
-      - name: Build and push Docker image
+      - name: Build and push with cache
         uses: docker/build-push-action@v5
         with:
           context: .
@@ -35,3 +40,7 @@ jobs:
           tags: |
             git.sakamoto.best/lolz/auto-stars:${{ steps.vars.outputs.SHORT_SHA }}
             git.sakamoto.best/lolz/auto-stars:latest
+          cache-from: type=registry,ref=git.sakamoto.best/lolz/auto-stars:buildcache
+          cache-to: type=registry,ref=git.sakamoto.best/lolz/auto-stars:buildcache,mode=max
+          build-args: |
+            BUILDKIT_INLINE_CACHE=1