Upgrade Companies page: stats, delete, status badge, dropdown menu

Server:
- companyService.stats() returns per-company agent/issue counts in one query pair
- companyService.remove() cascades deletes across all child tables in dependency order
- GET /companies/stats endpoint (board-accessible)
- DELETE /companies/:companyId endpoint (board-only)

UI:
- Companies page shows agent count, issue count, spend/budget, and created-at per card
- Company status shown as a colored badge (active/paused/archived)
- Three-dot dropdown menu with Rename and Delete Company actions
- Inline delete confirmation to prevent accidental data loss
- 'New Company' button opens onboarding wizard instead of inline form

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

ui/src/lib/queryKeys.ts

@@ -2,6 +2,7 @@ export const queryKeys = {
   companies: {
     all: ["companies"] as const,
     detail: (id: string) => ["companies", id] as const,
+    stats: ["companies", "stats"] as const,
   },
   agents: {
     list: (companyId: string) => ["agents", companyId] as const,