Add public key (npub) login support

- Backend: POST /auth/login-npub endpoint, JWT carries login method
- Backend: Enforce Lightning address lock for npub logins in claim/quote
- Frontend: LoginModal supports npub via new endpoint, clear copy
- Frontend: Track loginMethod, lock LN address editing for npub users
- Handle missing Lightning address for npub users with helpful message

Made-with: Cursor

backend/src/middleware/auth.ts

@@ -5,7 +5,7 @@ import { nip98Auth } from "./nip98.js";
 const BEARER_PREFIX = "Bearer ";
 
 /**
- * Accept either Bearer JWT or NIP-98. Sets req.nostr = { pubkey }.
+ * Accept either Bearer JWT or NIP-98. Sets req.nostr = { pubkey, method }.
  */
 export function authOrNip98(req: Request, res: Response, next: NextFunction): void {
   const auth = req.headers.authorization;
@@ -13,7 +13,7 @@ export function authOrNip98(req: Request, res: Response, next: NextFunction): vo
     const token = auth.slice(BEARER_PREFIX.length).trim();
     const payload = verifyJwt(token);
     if (payload) {
-      req.nostr = { pubkey: payload.pubkey, eventId: "" };
+      req.nostr = { pubkey: payload.pubkey, eventId: "", method: payload.method };
       next();
       return;
     }

backend/src/middleware/nip98.ts

@@ -8,6 +8,7 @@ const AUTH_SCHEME = "Nostr ";
 export interface NostrAuthPayload {
   pubkey: string;
   eventId: string;
+  method?: "nip98" | "npub";
 }
 
 declare global {