Pairing code auth, replace Facebook OAuth, public feed

- Add PairingCode model, POST /generate + /redeem + GET /status endpoints
- Remove facebookId from User, make metaId non-nullable
- Delete meta-web routes, link routes, meta-web-auth service
- Remove metaWeb config block and hasFacebookLink from responses
- Add optionalAuth middleware, make feed publicly accessible
- Resolve Twitch channel names for embed broadcastIds

src/types/api.ts

@@ -22,8 +22,6 @@ export interface UserProfileResponse {
   avatarUrl: string | null;
   bio: string;
   isPublic: boolean;
-  hasQuestLink: boolean;
-  hasFacebookLink: boolean;
 }
 
 export interface UpdateProfileBody {
@@ -32,19 +30,13 @@ export interface UpdateProfileBody {
   isPublic?: boolean;
 }
 
-export interface MetaWebCallbackBody {
+export interface PairingGenerateResponse {
   code: string;
-  state: string;
+  expiresAt: string;
 }
 
-export interface LinkQuestBody {
-  metaId: string;
-  nonce?: string;
-}
-
-export interface LinkFacebookBody {
+export interface PairingRedeemBody {
   code: string;
-  state: string;
 }
 
 // ── Providers ────────────────────────────────────────────