feat: email receipts and repair estimates

Backend:
- Server-side HTML email templates (receipt + estimate) with inline CSS
- POST /v1/transactions/:id/email-receipt with per-transaction rate limiting
- POST /v1/repair-tickets/:id/email-estimate with per-ticket rate limiting
- customerEmail field added to receipt and ticket detail responses
- Test email provider for API tests (logs instead of sending)

Frontend:
- POS payment dialog Email button enabled with inline email input
- Pre-fills customer email from linked account
- Repair ticket detail page has Email Estimate button with dialog
- Pre-fills from account email

Tests:
- 12 unit tests for email template renderers
- 8 API tests for email receipt/estimate endpoints and validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/backend/api-tests/suites/repairs.ts

@@ -510,4 +510,55 @@ suite('Repairs', { tags: ['repairs'] }, (t) => {
     const fileRes = await fetch(`${t.baseUrl}${signedRes.data.url}`)
     t.assert.equal(fileRes.status, 200)
   })
+
+  // ─── Email Estimate ─────────────────────────────────────────────────────────
+
+  t.test('emails a repair estimate', { tags: ['tickets', 'email'] }, async () => {
+    const ticket = await t.api.post('/v1/repair-tickets', {
+      customerName: 'Email Estimate Customer',
+      itemDescription: 'Broken Laptop',
+      problemDescription: 'Won\'t power on',
+      conditionIn: 'poor',
+      estimatedCost: 200,
+    })
+    await t.api.post(`/v1/repair-tickets/${ticket.data.id}/line-items`, {
+      itemType: 'labor',
+      description: 'Diagnostic fee',
+      qty: 1,
+      unitPrice: 50,
+    })
+
+    const res = await t.api.post(`/v1/repair-tickets/${ticket.data.id}/email-estimate`, { email: 'customer@test.com' })
+    t.assert.status(res, 200)
+    t.assert.equal(res.data.message, 'Estimate sent')
+    t.assert.equal(res.data.sentTo, 'customer@test.com')
+  })
+
+  t.test('rejects estimate email with invalid email', { tags: ['tickets', 'email', 'validation'] }, async () => {
+    const ticket = await t.api.post('/v1/repair-tickets', {
+      customerName: 'Bad Email Customer',
+      problemDescription: 'Test',
+      conditionIn: 'good',
+    })
+    const res = await t.api.post(`/v1/repair-tickets/${ticket.data.id}/email-estimate`, { email: 'bad' })
+    t.assert.status(res, 400)
+  })
+
+  t.test('returns 404 for estimate email on nonexistent ticket', { tags: ['tickets', 'email', 'validation'] }, async () => {
+    const res = await t.api.post('/v1/repair-tickets/00000000-0000-0000-0000-000000000000/email-estimate', { email: 'test@test.com' })
+    t.assert.status(res, 404)
+  })
+
+  t.test('ticket detail includes customerEmail from account', { tags: ['tickets', 'email'] }, async () => {
+    const acct = await t.api.post('/v1/accounts', { name: 'Repair Email Acct', email: 'repair@test.com', billingMode: 'consolidated' })
+    const ticket = await t.api.post('/v1/repair-tickets', {
+      customerName: 'Repair Email Acct',
+      accountId: acct.data.id,
+      problemDescription: 'Email test',
+      conditionIn: 'good',
+    })
+    const detail = await t.api.get(`/v1/repair-tickets/${ticket.data.id}`)
+    t.assert.status(detail, 200)
+    t.assert.equal(detail.data.customerEmail, 'repair@test.com')
+  })
 })