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`.

tests/utils/jwt.test.ts

@@ -17,7 +17,6 @@ describe('JWT utilities', () => {
   it('generates and verifies access tokens', () => {
     const token = generateAccessToken({
       sub: 'user-1',
-      id: 'user-1',
       plexId: 'plex-1',
       username: 'user',
       role: 'admin',
@@ -58,7 +57,6 @@ describe('JWT utilities', () => {
   it('decodes tokens without verification', () => {
     const token = generateAccessToken({
       sub: 'user-4',
-      id: 'user-4',
       plexId: 'plex-4',
       username: 'user',
       role: 'user',