feat: Feature 3.4 — Stripe integration with founder code system

Subscription billing:
- POST /api/stripe/checkout — creates Stripe Checkout session
- POST /api/stripe/webhook — handles lifecycle events (raw body)
- POST /api/stripe/portal — customer self-service management
- GET /api/stripe/status — current subscription info

Founder code system:
- Validates codes against env var list with expiry date
- Routes to founder Stripe Price IDs (locked rate for life)
- 4 price objects: analyst, analyst-founder, desk, desk-founder

Webhook events handled:
- checkout.session.completed → tier update + founder status
- customer.subscription.deleted → revert to free tier
- invoice.payment_failed → logged

Lazy Stripe init (no API key required at import time).
Raw body middleware for webhook signature verification.

16 new tests, 237 total (210 Node.js + 27 Python), all passing.
Phase 3 Web MVP COMPLETE. All roadmap features shipped.

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

package-lock.json

@@ -14,7 +14,8 @@
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+        "postgres": "^3.4.8",
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         "jest": "^30.3.0",
@@ -5065,6 +5066,23 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
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+      "license": "MIT",
+      "engines": {
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