Add PR validation workflow for analyze and test

No CI currently runs on pull requests — the only workflow triggers on
releases. This adds a lightweight, secrets-free workflow that runs
flutter analyze and flutter test on PRs to main and pushes to main.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/pr.yml

@@ -0,0 +1,26 @@
+name: Validate PR
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  validate:
+    name: Analyze & Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: 'stable'
+
+      - run: flutter pub get
+
+      - name: Analyze
+        run: flutter analyze
+
+      - name: Test
+        run: flutter test