Add TenantCustomTier system and fix BusinessEditModal feature loading

Backend:
- Add TenantCustomTier model for per-tenant feature overrides
- Update EntitlementService to check custom tier before plan features
- Add custom_tier action on TenantViewSet (GET/PUT/DELETE)
- Add Celery task for grace period management (30-day expiry)

Frontend:
- Add DynamicFeaturesEditor component for dynamic feature management
- Fix BusinessEditModal to load features from plan defaults when no custom tier
- Update limits (max_users, max_resources, etc.) to use featureValues
- Remove outdated canonical feature check from FeaturePicker (removes warning icons)
- Add useBillingPlans hook for accessing billing system data
- Add custom tier API functions to platform.ts

Features now follow consistent rules:
- Load from plan defaults when no custom tier exists
- Load from custom tier when one exists
- Reset to plan defaults when plan changes
- Save to custom tier on edit

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/hooks/usePublicPlans.ts

@@ -0,0 +1,156 @@
+/**
+ * Public Plans Hook
+ *
+ * Fetches public plans from the billing API for the marketing pricing page.
+ * This endpoint doesn't require authentication.
+ */
+
+import { useQuery } from '@tanstack/react-query';
+import axios from 'axios';
+import { API_BASE_URL } from '../api/config';
+
+// =============================================================================
+// Types
+// =============================================================================
+
+export interface Feature {
+  id: number;
+  code: string;
+  name: string;
+  description: string;
+  feature_type: 'boolean' | 'integer';
+}
+
+export interface PlanFeature {
+  id: number;
+  feature: Feature;
+  bool_value: boolean | null;
+  int_value: number | null;
+  value: boolean | number | null;
+}
+
+export interface Plan {
+  id: number;
+  code: string;
+  name: string;
+  description: string;
+  display_order: number;
+  is_active: boolean;
+}
+
+export interface PublicPlanVersion {
+  id: number;
+  plan: Plan;
+  version: number;
+  name: string;
+  is_public: boolean;
+  is_legacy: boolean;
+  price_monthly_cents: number;
+  price_yearly_cents: number;
+  transaction_fee_percent: string;
+  transaction_fee_fixed_cents: number;
+  trial_days: number;
+  is_most_popular: boolean;
+  show_price: boolean;
+  marketing_features: string[];
+  is_available: boolean;
+  features: PlanFeature[];
+  created_at: string;
+}
+
+// =============================================================================
+// API Client (no auth required)
+// =============================================================================
+
+const publicApiClient = axios.create({
+  baseURL: API_BASE_URL,
+  headers: {
+    'Content-Type': 'application/json',
+  },
+});
+
+// =============================================================================
+// API Functions
+// =============================================================================
+
+/**
+ * Fetch public plans from the billing catalog.
+ * No authentication required.
+ */
+export const fetchPublicPlans = async (): Promise<PublicPlanVersion[]> => {
+  const response = await publicApiClient.get<PublicPlanVersion[]>('/billing/plans/');
+  return response.data;
+};
+
+// =============================================================================
+// Hook
+// =============================================================================
+
+/**
+ * Hook to fetch public plans for the pricing page.
+ */
+export const usePublicPlans = () => {
+  return useQuery({
+    queryKey: ['publicPlans'],
+    queryFn: fetchPublicPlans,
+    staleTime: 5 * 60 * 1000, // 5 minutes
+    gcTime: 30 * 60 * 1000, // 30 minutes (formerly cacheTime)
+  });
+};
+
+// =============================================================================
+// Helper Functions
+// =============================================================================
+
+/**
+ * Format price from cents to dollars with currency symbol.
+ */
+export const formatPrice = (cents: number): string => {
+  if (cents === 0) return '$0';
+  return `$${(cents / 100).toFixed(0)}`;
+};
+
+/**
+ * Get a feature value from a plan version by feature code.
+ */
+export const getPlanFeatureValue = (
+  planVersion: PublicPlanVersion,
+  featureCode: string
+): boolean | number | null => {
+  const planFeature = planVersion.features.find(
+    (pf) => pf.feature.code === featureCode
+  );
+  return planFeature?.value ?? null;
+};
+
+/**
+ * Check if a plan has a boolean feature enabled.
+ */
+export const hasPlanFeature = (
+  planVersion: PublicPlanVersion,
+  featureCode: string
+): boolean => {
+  const value = getPlanFeatureValue(planVersion, featureCode);
+  return value === true;
+};
+
+/**
+ * Get an integer limit from a plan version.
+ * Returns 0 if not set (unlimited) or the actual limit.
+ */
+export const getPlanLimit = (
+  planVersion: PublicPlanVersion,
+  featureCode: string
+): number => {
+  const value = getPlanFeatureValue(planVersion, featureCode);
+  return typeof value === 'number' ? value : 0;
+};
+
+/**
+ * Format a limit value for display.
+ * 0 means unlimited.
+ */
+export const formatLimit = (value: number): string => {
+  if (value === 0) return 'Unlimited';
+  return value.toLocaleString();
+};