cleanup: remove MariaDB dependencies and files

- Remove MariaDB helper, schema, and initialization script
- Remove mysql2 dependency from package.json
- Update reset-admin.js to use SQLite DatabaseHelper
- Simplify .env.example to remove MariaDB configuration
- Update start-service.sh to use SQLite initialization
- Clean up all MariaDB references across codebase

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

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

package.json

@@ -7,7 +7,6 @@
     "start": "node server.js",
     "dev": "node server.js",
     "init-db": "node scripts/init-database.js",
-    "init-mariadb": "node scripts/init-mariadb.js",
     "build": "echo 'Build complete'"
   },
   "dependencies": {
@@ -16,7 +15,6 @@
     "express": "^4.18.2",
     "express-session": "^1.17.3",
     "multer": "^1.4.5-lts.1",
-    "mysql2": "^3.14.3",
     "sqlite3": "^5.1.6",
     "uuid": "^9.0.1"
   },