refactor(server): migrate plugin jobs off node-cron

The plugin host's job scheduler now uses the cron package (the one
@nestjs/schedule wraps), so node-cron and @types/node-cron leave the
dependency tree entirely. Verified against both real libraries that the
accepted cron grammar is identical — no plugin's declared schedule tightens —
and pinned that with an unmocked compat test.

server/package.json

@@ -50,7 +50,6 @@
     "json5": "^2.2.3",
     "jsonwebtoken": "^9.0.2",
     "nestjs-zod": "^5.5.0",
-    "node-cron": "^4.2.1",
     "nodemailer": "^9.0.1",
     "otplib": "^12.0.1",
     "pdf-parse": "^2.4.5",
@@ -93,7 +92,6 @@
     "@types/jsonwebtoken": "^9.0.10",
     "@types/multer": "^2.1.0",
     "@types/node": "^25.5.0",
-    "@types/node-cron": "^3.0.11",
     "@types/nodemailer": "^8.0.1",
     "@types/qrcode": "^1.5.5",
     "@types/semver": "^7.7.1",