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- Remove outdated canonical feature check from FeaturePicker (removes warning icons)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/components/__tests__/FloatingHelpButton.test.tsx

@@ -0,0 +1,86 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import { MemoryRouter } from 'react-router-dom';
+import FloatingHelpButton from '../FloatingHelpButton';
+
+// Mock react-i18next
+vi.mock('react-i18next', () => ({
+  useTranslation: () => ({
+    t: (key: string, defaultValue?: string) => defaultValue || key,
+  }),
+}));
+
+describe('FloatingHelpButton', () => {
+  const renderWithRouter = (initialPath: string) => {
+    return render(
+      <MemoryRouter initialEntries={[initialPath]}>
+        <FloatingHelpButton />
+      </MemoryRouter>
+    );
+  };
+
+  it('renders help link on dashboard', () => {
+    renderWithRouter('/dashboard');
+    const link = screen.getByRole('link');
+    expect(link).toBeInTheDocument();
+  });
+
+  it('links to correct help page for dashboard', () => {
+    renderWithRouter('/dashboard');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/dashboard');
+  });
+
+  it('links to correct help page for scheduler', () => {
+    renderWithRouter('/scheduler');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/scheduler');
+  });
+
+  it('links to correct help page for services', () => {
+    renderWithRouter('/services');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/services');
+  });
+
+  it('links to correct help page for resources', () => {
+    renderWithRouter('/resources');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/resources');
+  });
+
+  it('links to correct help page for settings', () => {
+    renderWithRouter('/settings/general');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/settings/general');
+  });
+
+  it('returns null on help pages', () => {
+    const { container } = renderWithRouter('/help/dashboard');
+    expect(container.firstChild).toBeNull();
+  });
+
+  it('has aria-label', () => {
+    renderWithRouter('/dashboard');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('aria-label', 'Help');
+  });
+
+  it('has title attribute', () => {
+    renderWithRouter('/dashboard');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('title', 'Help');
+  });
+
+  it('links to default help for unknown routes', () => {
+    renderWithRouter('/unknown-route');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help');
+  });
+
+  it('handles dynamic routes by matching prefix', () => {
+    renderWithRouter('/customers/123');
+    const link = screen.getByRole('link');
+    expect(link).toHaveAttribute('href', '/help/customers');
+  });
+});