feat: update frontend for account-based subscriptions

Replace all team_id/team_admin references with account_id/owner across
types, store, hooks, API clients, components, and pages. Add new
AccountSettingsPage, UpgradePrompt, CheckoutButton, useSubscription
hook, and accounts API client. AuthStore now parallel-fetches account
and subscription data alongside user profile.

Also fix folder sidebar not refreshing after tree deletion by
dispatching the folder-changed event in handleDeleteTree.

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

frontend/src/api/categories.ts

@@ -2,9 +2,9 @@ import apiClient from './client'
 import type { Category, CategoryListItem, CategoryCreate, CategoryUpdate } from '@/types'
 
 export const categoriesApi = {
-  async list(includeInactive = false, teamOnly = false): Promise<CategoryListItem[]> {
+  async list(includeInactive = false, accountOnly = false): Promise<CategoryListItem[]> {
     const response = await apiClient.get<CategoryListItem[]>('/categories', {
-      params: { include_inactive: includeInactive, team_only: teamOnly },
+      params: { include_inactive: includeInactive, account_only: accountOnly },
     })
     return response.data
   },