feat: self-serve signup Phase 2 (frontend cutover) (#162)

Co-authored-by: Michael Chihlas <michael@resolutionflow.com>
Co-committed-by: Michael Chihlas <michael@resolutionflow.com>

frontend/src/hooks/useFeature.test.ts

@@ -0,0 +1,44 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { useFeature } from './useFeature'
+import { useBillingStore } from '@/store/billingStore'
+
+describe('useFeature', () => {
+  beforeEach(() => {
+    useBillingStore.setState({
+      subscription: null,
+      planBilling: null,
+      planLimits: {},
+      enabledFeatures: {},
+      isLoading: false,
+      error: null,
+    })
+  })
+
+  it('returns false when flag absent', () => {
+    const { result } = renderHook(() => useFeature('does_not_exist'))
+    expect(result.current).toBe(false)
+  })
+
+  it('returns true when flag is enabled', () => {
+    useBillingStore.setState({ enabledFeatures: { ai_builder: true } })
+    const { result } = renderHook(() => useFeature('ai_builder'))
+    expect(result.current).toBe(true)
+  })
+
+  it('returns false when flag is explicitly disabled', () => {
+    useBillingStore.setState({ enabledFeatures: { ai_builder: false } })
+    const { result } = renderHook(() => useFeature('ai_builder'))
+    expect(result.current).toBe(false)
+  })
+
+  it('updates when store changes (subscribes to store)', () => {
+    const { result } = renderHook(() => useFeature('foo'))
+    expect(result.current).toBe(false)
+
+    act(() => {
+      useBillingStore.setState({ enabledFeatures: { foo: true } })
+    })
+    expect(result.current).toBe(true)
+  })
+})