ci: split into fast analyze + slow release build with path gating

analyze runs on every push/PR (fast check).
release-apk only fires on push to master or workflow_dispatch (slow build).
Doc-only pushes no longer trigger any CI run.
workflow_dispatch triggers both jobs unconditionally.

.github/workflows/ci.yaml

@@ -7,9 +7,9 @@ on:
       - 'lib/**.dart'
       - 'test/**.dart'
       - 'android/**'
-      - 'tool/**'
       - 'pubspec.yaml'
       - 'pubspec.lock'
+      - 'images/**'
   pull_request:
     branches: [ master ]
   workflow_dispatch:
@@ -42,6 +42,7 @@ jobs:
     name: Release APK
     runs-on: flutter-android
     needs: [analyze]
+    if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
     steps:
       - uses: actions/checkout@v4