feat: add real Stripe integration, e2e tests, and Pi deployment

Replace documentation-only repo with working code:

- Stripe integration: webhook handler (8 event types), billing API
  (customers, checkout, payments, subscriptions, invoices)
- Express API server with health endpoint, structured logging
- E2E tests (Playwright): health, webhook signature verification,
  billing API validation
- Unit tests: webhook event handler coverage for all event types
- Pi deployment: deploy.sh (rsync + systemd), NGINX load balancer
  across Pi cluster, Docker support
- CI/CD: test workflow, Pi deploy workflow, updated auto-deploy
  and self-healing to run real tests before deploying
- Move resume docs to docs/ to separate code from documentation

https://claude.ai/code/session_01Mf5Pg82fV6BTRS9GnpV7nr

tests/e2e/billing-api.spec.js

@@ -0,0 +1,38 @@
+const { test, expect } = require('@playwright/test');
+
+const BASE_URL = process.env.BASE_URL || 'http://localhost:3000';
+
+test.describe('Billing API E2E', () => {
+  test('POST /api/customers rejects missing email', async ({ request }) => {
+    const res = await request.post(`${BASE_URL}/api/customers`, {
+      data: { name: 'Test User' },
+      headers: { 'Content-Type': 'application/json' },
+    });
+    expect(res.status()).toBe(400);
+
+    const body = await res.json();
+    expect(body.error).toBe('email is required');
+  });
+
+  test('POST /api/checkout rejects missing fields', async ({ request }) => {
+    const res = await request.post(`${BASE_URL}/api/checkout`, {
+      data: {},
+      headers: { 'Content-Type': 'application/json' },
+    });
+    expect(res.status()).toBe(400);
+
+    const body = await res.json();
+    expect(body.error).toContain('required');
+  });
+
+  test('POST /api/payments rejects missing fields', async ({ request }) => {
+    const res = await request.post(`${BASE_URL}/api/payments`, {
+      data: { customerId: 'cust_123' },
+      headers: { 'Content-Type': 'application/json' },
+    });
+    expect(res.status()).toBe(400);
+
+    const body = await res.json();
+    expect(body.error).toContain('required');
+  });
+});