feat(center): user display name + GET/PATCH /auth/me

- User.name column, defaults to email on register
- GET /auth/me, PATCH /auth/me to view/change own name (api-key exempt)
- login + guild members responses now include name

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/entities/user.entity.ts

@@ -8,6 +8,9 @@ export class User {
   @Column({ unique: true })
   email!: string;
 
+  @Column({ type: 'varchar', length: 120, nullable: true })
+  name!: string | null;
+
   @Column()
   passwordHash!: string;