feat(L1): modular widget dashboard — 15 configurable widgets

Replaces monolithic AdminDashboard/ClientDashboard with a per-user
configurable widget grid. 15 widget types: ProductionStats, QueueStatus,
RecentRenders, CostOverview, WorkerStatus, KPISummary, OrderThroughput,
Revenue, ItemStatus, ProcessingTimes, RenderTimeByOutputType,
OutputTypeUsage, TopProducts, OrdersByUser, RenderBackendStats.

DashboardTimeframeContext provides shared timeframe state. Dashboard
config persisted in DB via GET/PUT /api/dashboard/config.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/api/dashboard.ts

@@ -6,6 +6,16 @@ export type WidgetType =
   | 'RecentRenders'
   | 'CostOverview'
   | 'WorkerStatus'
+  | 'KPISummary'
+  | 'OrderThroughput'
+  | 'RevenueChart'
+  | 'ItemStatus'
+  | 'ProcessingTimes'
+  | 'RenderTimeByOutputType'
+  | 'OutputTypeUsage'
+  | 'TopProducts'
+  | 'OrdersByUser'
+  | 'RenderBackendStats'
 
 export interface WidgetPosition {
   col: number