Trigger badge sync only after build workflow completes

Use workflow_run instead of push trigger to ensure badges
update after images are actually built.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/sync-readme-badges.yaml

@@ -1,11 +1,10 @@
 name: Sync README Badges
 
 on:
-  push:
-    paths:
-      - 'Dockerfile.android'
-      - 'Dockerfile'
-      - 'Dockerfile.linux'
+  workflow_run:
+    workflows: ["Build and Push Flutter SDK Image"]
+    types:
+      - completed
   workflow_dispatch:
 
 jobs: