polish(ops): friendly not-found message on cross-space area-lead update

updateAreaLead used .single(), which errors (raw PostgREST message) rather than
returning null when the id isn't in the caller's space. Switch to .maybeSingle()
so the existing 'Area lead not found' guard is reached, matching deleteAreaLead.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

lib/actions/area-leads.ts

@@ -121,9 +121,11 @@ export async function updateAreaLead(
     .eq('id', v.data.id)
     .eq('space_id', member.space_id)
     .select()
-    .single()
+    .maybeSingle()
 
   if (error) return { error: error.message }
+  // A cross-space / missing id matches 0 rows; surface the friendly message
+  // (maybeSingle returns null rather than erroring, unlike single()).
   if (!data) return { error: 'Area lead not found' }
 
   await logActivity(supabase, member, 'updated', 'area_lead', v.data.id)