Expose POST /api/finance/portal/ so authenticated users can open Stripe's hosted portal for plan changes, payment methods, and cancellations (chat_web_app#33 companion).
## Summary - Closes #21 — new Django `finance` app with Stripe as payment provider - Subscription price defaults to **$10 USD / month** via `SUBSCRIPTION_PRICE_AMOUNT_CENTS = 1000` in `settings.py` (env-overridable) - Persists **Invoice** and **Payment** rows; both registered in Django admin (with payment inline on invoices) - Checkout Session API redirects users to Stripe hosted payment; webhook verifies signatures and upserts ledger idempotently ## API - `POST /api/finance/checkout/` — JWT auth → `{ checkout_url, session_id }` - `GET /api/finance/invoices/` / `GET /api/finance/payments/` — own records - `POST /api/finance/webhooks/stripe/` — Stripe signature-verified webhook ## Config Documented in `.env.example` / `.env.prod.example`: `STRIPE_SECRET_KEY`, `STRIPE_PUBLISHABLE_KEY`, `STRIPE_WEBHOOK_SECRET`, optional `STRIPE_PRICE_ID`, `FRONTEND_BASE_URL` ## Test plan - [x] `uv run python manage.py test finance` (17 tests) - [ ] Set Stripe test keys locally; create checkout session; complete payment in Stripe test mode - [ ] Confirm Invoice/Payment appear in `/admin/` - [ ] Point Stripe webhook to `/api/finance/webhooks/stripe/` and verify `checkout.session.completed` / `invoice.paid`Reviewed-on: #23
westfarn