feat(health): add health.json with version info

- Generate health.json from pubspec.yaml at build time
- health.html fetches and displays JSON with version, title, status
- Added tool/generate_health_json.dart script

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Dockerfile

@@ -15,6 +15,9 @@ COPY . .
 # Generate code with build_runner
 RUN dart run build_runner build --delete-conflicting-outputs
 
+# Generate health.json with version info
+RUN dart run tool/generate_health_json.dart
+
 # Build for web release with production configuration
 # These URLs enable authentication (requiresAuth = true when URL contains schweitz.net)
 RUN flutter build web --release \