Remove redundant id field from JWT payloads

Drop the duplicated `id` alias from JWT payloads and related token generation across auth providers and endpoints. The TokenPayload interface no longer includes `id`; middleware now derives `user.id` from `sub` when attaching the authenticated user to requests. Update tests accordingly. This reduces redundancy and ensures the canonical user identifier is `sub`.

src/app/api/auth/plex/switch-profile/route.ts

@@ -167,7 +167,6 @@ export async function POST(request: NextRequest) {
     // Generate JWT tokens
     const accessToken = generateAccessToken({
       sub: user.id,
-      id: user.id,
       plexId: user.plexId,
       username: user.plexUsername,
       role: user.role,