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>

tool/generate_health_json.dart

@@ -0,0 +1,49 @@
+#!/usr/bin/env dart
+// Generates web/health.json from pubspec.yaml
+// Run: dart run tool/generate_health_json.dart
+
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:yaml/yaml.dart';
+
+void main() {
+  final pubspecFile = File('pubspec.yaml');
+  if (!pubspecFile.existsSync()) {
+    stderr.writeln('Error: pubspec.yaml not found');
+    exit(1);
+  }
+
+  final pubspecContent = pubspecFile.readAsStringSync();
+  final pubspec = loadYaml(pubspecContent) as YamlMap;
+
+  final name = pubspec['name'] as String;
+  final description = pubspec['description'] as String? ?? '';
+  final versionString = pubspec['version'] as String;
+
+  // Parse version: "1.0.3+1" -> version="1.0.3", buildNumber=1
+  final versionParts = versionString.split('+');
+  final version = versionParts[0];
+  final buildNumber = versionParts.length > 1 ? int.parse(versionParts[1]) : 0;
+
+  final health = {
+    'status': 'healthy',
+    'name': name,
+    'title': description,
+    'version': version,
+    'buildNumber': buildNumber,
+    'fullVersion': '$version+$buildNumber',
+  };
+
+  final webDir = Directory('web');
+  if (!webDir.existsSync()) {
+    webDir.createSync(recursive: true);
+  }
+
+  final healthFile = File('web/health.json');
+  healthFile.writeAsStringSync(
+    const JsonEncoder.withIndent('  ').convert(health),
+  );
+
+  print('Generated web/health.json with version $version+$buildNumber');
+}