feat(l1): drafts + tickets pages + coverage banner + seat counter widget

L1DraftsPage is a Phase 1 placeholder (AI drafts arrive in Phase 2).
L1TicketsPage replaces the stub with a status-filterable internal-tickets
queue. L1CoverageBanner renders inside L1RouteGuard so every /l1/* page
shows it for engineer-coverers (hidden for native L1). SeatCounterWidget
+ /api/seats.ts surface engineer + L1 seat usage from the /accounts/me/
seats endpoint (T9).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/l1/L1DraftsPage.tsx

@@ -5,8 +5,10 @@ export default function L1DraftsPage() {
     <div className="overflow-y-auto h-full">
       <PageMeta title="My Drafts" />
       <div className="max-w-4xl mx-auto px-6 pt-12 pb-12">
-        <h1 className="font-heading text-2xl font-bold">My Drafts</h1>
-        <p className="text-muted-foreground mt-2">Loading…</p>
+        <h1 className="font-heading text-2xl font-bold mb-2">My AI drafts</h1>
+        <p className="text-muted-foreground">
+          AI-built drafts you've created will show here once AI build is enabled (Phase 2).
+        </p>
       </div>
     </div>
   )