fix: resolve all TypeScript errors via proper Express 5 typed route params

- Add StringParams = Record<string, string> to types.ts
- Use Request<StringParams> in all route handlers across 14 files
- Clean up earlier as-cast workarounds in places.ts and admin.ts
- tsconfig.json: keep original (removed bad 'types:node' addition)
- package.json: restore @types/express back to ^5.0.6

server/package.json

@@ -29,7 +29,7 @@
     "@types/bcryptjs": "^2.4.6",
     "@types/better-sqlite3": "^7.6.13",
     "@types/cors": "^2.8.19",
-    "@types/express": "^4.17.25",
+    "@types/express": "^5.0.6",
     "@types/jsonwebtoken": "^9.0.10",
     "@types/multer": "^2.1.0",
     "@types/node": "^25.5.0",