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/api/seats.ts

@@ -0,0 +1,17 @@
+import { apiClient } from './client'
+
+export interface SeatCheck {
+  available: boolean
+  current: number
+  limit: number | null
+  role: 'engineer' | 'l1_tech'
+}
+
+export interface SeatUsage {
+  engineer: SeatCheck
+  l1_tech: SeatCheck
+}
+
+export const seatsApi = {
+  getUsage: () => apiClient.get<SeatUsage>('/accounts/me/seats').then((r) => r.data),
+}