fix(ux): resolve Soulseek search spinner wedge and onboarding 'already taken' dead-end

- Soulseek search relied solely on an SSE 'complete' event to clear its
  spinner; if that event was dropped (connection blip, backend never emits it)
  the search UI spun forever. Add a 45s fallback that force-completes the
  search so the user sees whatever results arrived; late results still stream
  in via the store subscription.
- Onboarding's 'username already taken' path told the user to refresh, which
  can't recover the half-created account (the token never persisted). Instead
  attempt a login with the same credentials and continue: resume at step 2 if
  onboarding is unfinished, route home if already complete, or send to the
  normal sign-in for a 2FA account. A genuine password mismatch now gets a
  clear 'sign in instead' message rather than a dead end.

frontend/app/onboarding/page.tsx

@@ -104,9 +104,27 @@ export default function OnboardingPage() {
             const message = err instanceof Error ? err.message : String(err);
             // Check if user already exists
             if (message?.includes("already taken")) {
-                setError(
-                    "Username already taken. If this is you, please refresh and continue where you left off.",
-                );
+                // Usually a refresh/retry race: the account was created but the
+                // token never persisted client-side. Rather than dead-end on a
+                // "refresh" instruction that can't recover the session, try
+                // logging in with the same credentials and continue.
+                try {
+                    const user = await api.login(username, password);
+                    if (user.requires2FA) {
+                        router.push("/login");
+                        return;
+                    }
+                    if (user.onboardingComplete) {
+                        router.push("/");
+                        return;
+                    }
+                    setStep(2);
+                    return;
+                } catch {
+                    setError(
+                        "That username already exists and the password didn't match. If it's your account, sign in instead.",
+                    );
+                }
             } else {
                 setError(message || "Failed to create account");
             }

frontend/features/search/hooks/useSoulseekSearch.ts

@@ -124,6 +124,18 @@ export function useSoulseekSearch({
         };
     }, [query, soulseekEnabled]);
 
+    // Fallback completion: the SSE "complete" event can be dropped (connection
+    // blip, or the backend never emits it). Without a terminal signal
+    // isSoulseekPolling stays true and the search UI spins forever. Force the
+    // search complete after a ceiling so the user sees whatever results arrived
+    // instead of an endless spinner; late results still stream in via the store
+    // subscription, only the spinner is resolved.
+    useEffect(() => {
+        if (!hasActiveSearch || isComplete) return;
+        const timeout = setTimeout(() => setIsComplete(true), 45000);
+        return () => clearTimeout(timeout);
+    }, [hasActiveSearch, isComplete]);
+
     const handleDownload = useCallback(async (result: SoulseekResult) => {
         const downloadKey = `${result.username}:${result.path}`;
         try {