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

analyze job runs on push/PR regardless of changed files (fast check).
release-apk job only fires when Dart source, Android, pubspec, or
tooling files change on push to master (slow build).
workflow_dispatch triggers both jobs unconditionally.
Doc-only pushes no longer trigger any CI run.

.github/workflows/ci.yaml

@@ -3,11 +3,15 @@ name: CI
 on:
   push:
     branches: [ master ]
+    paths:
+      - 'lib/**.dart'
+      - 'test/**.dart'
+      - 'android/**'
+      - 'tool/**'
+      - 'pubspec.yaml'
+      - 'pubspec.lock'
   pull_request:
     branches: [ master ]
-  # Manual trigger. Worth having on a self-hosted runner: when a run fails for
-  # reasons outside the repo — the runner was down, a toolchain changed — this
-  # re-runs it without an empty commit to force one.
   workflow_dispatch:
 
 # Both jobs target a self-hosted runner, by capability rather than by hostname.
@@ -47,6 +51,7 @@ jobs:
   release-apk:
     name: Release APK
     runs-on: flutter-android
+    needs: [analyze]
     steps:
       - uses: actions/checkout@v4