Fix all backend lint errors and security vulnerabilities

Backend lint (4 errors fixed):
- auth.ts: suppress @typescript-eslint/no-namespace on Express global
  augmentation (legitimate TS pattern for extending Request type)
- clients.ts: remove unnecessary \. escape in regex character class
- devices.ts: remove unnecessary \- escape by moving hyphen to front [-:]
- PollerService.ts: add comment to empty catch block

Security audit (high/critical CVEs fixed):
- frontend: bump axios (critical SSRF), lodash (high injection),
  follow-redirects (moderate) via npm audit fix
- backend: bump nodemailer 6.x → 8.0.5 (fixes 4 SMTP injection CVEs)

backend/package-lock.json

@@ -20,7 +20,7 @@
         "ioredis": "^5.3.2",
         "jsonwebtoken": "^9.0.2",
         "morgan": "^1.10.0",
-        "nodemailer": "^6.9.13",
+        "nodemailer": "^8.0.5",
         "pg": "^8.11.3",
         "socket.io": "^4.6.1",
         "ssh2": "^1.14.0",
@@ -3055,9 +3055,9 @@
       }
     },
     "node_modules/nodemailer": {
-      "version": "6.10.1",
-      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-6.10.1.tgz",
-      "integrity": "sha512-Z+iLaBGVaSjbIzQ4pX6XV41HrooLsQ10ZWPUehGmuantvzWoDVBnmsdUcOIDM1t+yPor5pDhVlDESgOMEGxhHA==",
+      "version": "8.0.5",
+      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-8.0.5.tgz",
+      "integrity": "sha512-0PF8Yb1yZuQfQbq+5/pZJrtF6WQcjTd5/S4JOHs9PGFxuTqoB/icwuB44pOdURHJbRKX1PPoJZtY7R4VUoCC8w==",
       "license": "MIT-0",
       "engines": {
         "node": ">=6.0.0"