refactor: remove all JWT-related code and references

JWT was never used - auth uses X-User-Id header. Removes jwt.ts utility,
jsonwebtoken dependency, stubbed refresh/logout endpoints, and updates
all docs (PUML diagrams, api-routes, tex, CLAUDE.md) accordingly.

apps/server/package.json

@@ -14,7 +14,6 @@
     "dotenv": "^16.4.7",
     "express": "^5.2.1",
     "ical.js": "^2.2.1",
-    "jsonwebtoken": "^9.0.3",
     "mongoose": "^9.1.1",
     "openai": "^6.15.0",
     "pino": "^10.1.1",
@@ -27,7 +26,6 @@
     "@types/express": "^5.0.6",
     "@types/ical": "^0.8.3",
     "@types/jest": "^30.0.0",
-    "@types/jsonwebtoken": "^9.0.10",
     "@types/node": "^24.10.1",
     "jest": "^30.2.0",
     "pino-pretty": "^13.1.3",