fix: use maybeSingle for profile share route to avoid PGRST116 crash

When no unified profile exists yet, .single() throws instead of
returning null. Switch to .maybeSingle() so the existing 404 handler
responds gracefully.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: devakone

apps/web/src/app/api/share/[format]/[userId]/route.tsx

@@ -65,7 +65,7 @@ export async function GET(
       .from("user_profiles")
       .select("persona_id, persona_name, persona_tagline, persona_confidence, total_repos, total_commits, axes_json, narrative_json")
       .eq("user_id", userId)
-      .single();
+      .maybeSingle();
 
     if (error) {
       console.error("Supabase error:", error);