feat(sales): add /contact-sales form + landing page CTA

Public Talk-to-Sales surface and a "See pricing" hero CTA on the marketing
landing page. Phase 2 Task 43 of self-serve signup.

- frontend/src/api/sales.ts: salesApi.createLead -> POST /sales-leads.
- ContactSalesPage at /contact-sales (public, gated by self_serve_enabled
  with a 404-style fallback). Form fields: name, work email, company,
  team size (1-2 / 3-5 / 6-10 / 11-25 / 26+), and an optional
  "what brought you here?" textarea -> message. Submit button disabled
  while in flight to block duplicate submissions.
- Confirmation surface replaces the form on success. Calendly block is
  hidden when VITE_CALENDLY_URL is unset.
- detectSource(): 'pricing_page' if document.referrer contains '/pricing',
  else 'landing_page'. Server emits the canonical PostHog
  talk_to_sales_form_submitted event with this source.
- LandingPage: new "See pricing" hero CTA gated by useAppConfig().
  self_serve_enabled.
- frontend/.env.example + Dockerfile: VITE_CALENDLY_URL ARG/ENV.
- Tests: ContactSalesPage submit/confirmation, Calendly hide-when-unset,
  in-flight de-dup, 404 when self-serve off; LandingPage CTA on/off.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/pages/__tests__/ContactSalesPage.test.tsx

@@ -0,0 +1,146 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { render, screen, fireEvent, waitFor } from '@testing-library/react'
+import { MemoryRouter } from 'react-router-dom'
+import { HelmetProvider } from 'react-helmet-async'
+
+import { ContactSalesPage } from '../ContactSalesPage'
+import { salesApi } from '@/api/sales'
+import {
+  __resetAppConfigCache,
+  __setAppConfigCache,
+} from '@/hooks/useAppConfig'
+
+vi.mock('@/api/sales', () => ({
+  salesApi: {
+    createLead: vi.fn(),
+  },
+}))
+
+function renderPage() {
+  return render(
+    <HelmetProvider>
+      <MemoryRouter initialEntries={['/contact-sales']}>
+        <ContactSalesPage />
+      </MemoryRouter>
+    </HelmetProvider>,
+  )
+}
+
+function fillRequiredFields() {
+  fireEvent.change(screen.getByTestId('cs-name'), { target: { value: 'Jane Doe' } })
+  fireEvent.change(screen.getByTestId('cs-email'), { target: { value: 'jane@acme.com' } })
+  fireEvent.change(screen.getByTestId('cs-company'), { target: { value: 'Acme MSP' } })
+}
+
+describe('ContactSalesPage', () => {
+  beforeEach(() => {
+    __resetAppConfigCache()
+    __setAppConfigCache({
+      self_serve_enabled: true,
+      oauth_providers: [],
+    })
+    vi.clearAllMocks()
+    vi.unstubAllEnvs()
+  })
+
+  it('submits form and shows confirmation', async () => {
+    vi.stubEnv('VITE_CALENDLY_URL', 'https://calendly.com/resolutionflow/sales')
+    vi.mocked(salesApi.createLead).mockResolvedValue({
+      id: 'fake-uuid',
+      status: 'received',
+    })
+
+    renderPage()
+
+    fillRequiredFields()
+    fireEvent.change(screen.getByTestId('cs-team-size'), { target: { value: '11-25' } })
+    fireEvent.change(screen.getByTestId('cs-message'), {
+      target: { value: 'Looking at Enterprise pricing.' },
+    })
+
+    fireEvent.click(screen.getByTestId('cs-submit'))
+
+    await waitFor(() => {
+      expect(salesApi.createLead).toHaveBeenCalledTimes(1)
+    })
+
+    const payload = vi.mocked(salesApi.createLead).mock.calls[0][0]
+    expect(payload).toMatchObject({
+      name: 'Jane Doe',
+      email: 'jane@acme.com',
+      company: 'Acme MSP',
+      team_size: '11-25',
+      message: 'Looking at Enterprise pricing.',
+    })
+    // Default source is landing_page (no /pricing in referrer in jsdom).
+    expect(payload.source).toBe('landing_page')
+
+    // Confirmation surface replaces the form.
+    await waitFor(() => {
+      expect(screen.getByTestId('contact-sales-confirmation')).toBeInTheDocument()
+    })
+    expect(screen.queryByTestId('contact-sales-form')).not.toBeInTheDocument()
+    expect(screen.getByText(/Thanks/i)).toBeInTheDocument()
+  })
+
+  it('hides Calendly section when VITE_CALENDLY_URL unset', async () => {
+    vi.stubEnv('VITE_CALENDLY_URL', '')
+    vi.mocked(salesApi.createLead).mockResolvedValue({
+      id: 'fake-uuid',
+      status: 'received',
+    })
+
+    renderPage()
+    fillRequiredFields()
+    fireEvent.click(screen.getByTestId('cs-submit'))
+
+    await waitFor(() => {
+      expect(screen.getByTestId('contact-sales-confirmation')).toBeInTheDocument()
+    })
+
+    expect(screen.queryByTestId('calendly-block')).not.toBeInTheDocument()
+    expect(screen.queryByTestId('calendly-link')).not.toBeInTheDocument()
+  })
+
+  it('disables submit button while in flight to prevent duplicate submissions', async () => {
+    let resolveSubmit: (() => void) | null = null
+    vi.mocked(salesApi.createLead).mockImplementation(
+      () =>
+        new Promise((resolve) => {
+          resolveSubmit = () => resolve({ id: 'fake-uuid', status: 'received' })
+        }),
+    )
+
+    renderPage()
+    fillRequiredFields()
+
+    const submit = screen.getByTestId('cs-submit') as HTMLButtonElement
+    fireEvent.click(submit)
+
+    await waitFor(() => {
+      expect(submit.disabled).toBe(true)
+    })
+
+    // A second click while in flight should be a no-op.
+    fireEvent.click(submit)
+    expect(salesApi.createLead).toHaveBeenCalledTimes(1)
+
+    resolveSubmit?.()
+    await waitFor(() => {
+      expect(screen.getByTestId('contact-sales-confirmation')).toBeInTheDocument()
+    })
+  })
+
+  it('returns 404 when self_serve_enabled is false', () => {
+    __resetAppConfigCache()
+    __setAppConfigCache({
+      self_serve_enabled: false,
+      oauth_providers: [],
+    })
+
+    renderPage()
+
+    expect(screen.getByTestId('contact-sales-not-found')).toBeInTheDocument()
+    expect(screen.queryByTestId('contact-sales-form')).not.toBeInTheDocument()
+  })
+})