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/src/services/AuthService.ts

@@ -1,6 +1,5 @@
-import { User, CreateUserDTO, LoginDTO, AuthResponse } from "@calchat/shared";
+import { CreateUserDTO, LoginDTO, AuthResponse } from "@calchat/shared";
 import { UserRepository } from "./interfaces";
-import * as jwt from "../utils/jwt";
 import * as password from "../utils/password";
 
 export class AuthService {
@@ -46,11 +45,4 @@ export class AuthService {
     return { user, accessToken: "" };
   }
 
-  async refreshToken(refreshToken: string): Promise<AuthResponse> {
-    throw new Error("Not implemented");
-  }
-
-  async logout(userId: string): Promise<void> {
-    throw new Error("Not implemented");
-  }
 }