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

frontend/src/App.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect, useCallback } from "react";
 import { BrowserRouter, Routes, Route } from "react-router-dom";
-import { getToken, getAuthMe, clearToken } from "./api";
+import { getToken, getAuthMe, clearToken, type LoginMethod } from "./api";
 import { Header } from "./components/Header";
 import { Footer } from "./components/Footer";
 import { ClaimWizard } from "./components/ClaimWizard";
@@ -26,19 +26,29 @@ const FaucetSvg = () => (
 
 export default function App() {
   const [pubkey, setPubkey] = useState<string | null>(null);
+  const [loginMethod, setLoginMethod] = useState<LoginMethod | null>(null);
   const [statsRefetchTrigger, setStatsRefetchTrigger] = useState(0);
 
   useEffect(() => {
     const token = getToken();
     if (!token) return;
     getAuthMe()
-      .then((r) => setPubkey(r.pubkey))
+      .then((r) => {
+        setPubkey(r.pubkey);
+        setLoginMethod(r.method ?? "nip98");
+      })
       .catch(() => {
         clearToken();
         setPubkey(null);
+        setLoginMethod(null);
       });
   }, []);
 
+  const handlePubkeyChange = useCallback((pk: string | null, method?: LoginMethod) => {
+    setPubkey(pk);
+    setLoginMethod(pk ? (method ?? "nip98") : null);
+  }, []);
+
   const handleClaimSuccess = useCallback(() => {
     setStatsRefetchTrigger((t) => t + 1);
   }, []);
@@ -74,7 +84,7 @@ export default function App() {
                       <FaucetSvg />
                       <h1>Sats Faucet</h1>
                     </div>
-                    <ClaimWizard pubkey={pubkey} onPubkeyChange={setPubkey} onClaimSuccess={handleClaimSuccess} />
+                    <ClaimWizard pubkey={pubkey} loginMethod={loginMethod} onPubkeyChange={handlePubkeyChange} onClaimSuccess={handleClaimSuccess} />
                   </main>
                   <aside className="sidebar sidebar-right">
                     <StatsSection refetchTrigger={statsRefetchTrigger} />