feat: Tink open banking demo — 6-step API walkthrough

Demonstrates the full Tink integration flow for open banking:
  Step 1 — Client credentials auth (app token)
  Step 2 — Create Tink user with external_user_id
  Step 3 — Connect bank via Tink Link OAuth redirect
  Step 4 — List accounts (v2 endpoint)
  Step 5 — List transactions (v2 endpoint, cursor pagination)
  Step 6 — Webhooks (register endpoint, receive events)

Built with Python / FastAPI + Jinja2 templates.
Each step shows live JSON responses, cURL examples and API version badges.
Includes server-side token store (prevents session cookie overflow),
asyncio lock on OAuth callback, and demo mode with realistic mock data.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

README.md

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+# MoneyCapp × Tink API Demo
+
+"Sales-y Swagger" — step-for-step gennemgang af Tink integrationsflowet med live JSON responses.
+
+## Hvad det er
+
+En hosted demo-app der viser hele Tink onboarding-flowet:
+
+| Step | Endpoint | Version |
+|------|----------|---------|
+| 1 | POST `/api/v1/oauth/token` — Client Credentials | v1 |
+| 2 | POST `/api/v1/user/create` — Opret bruger | v1 |
+| 3 | Tink Link redirect — Tilslut bank | Link v1 |
+| 4 | GET `/data/v2/accounts` — Konti med balances | **v2** |
+| 5 | GET `/data/v2/transactions` — Transaktioner | **v2** |
+| 6 | GET `/events/v2/account-transactions` + webhooks | **v2** |
+
+## Quick start (lokal dev)
+
+```bash
+cp .env.example .env
+# Udfyld TINK_CLIENT_ID og TINK_CLIENT_SECRET fra Tink Console
+# Tilføj http://localhost:8000/callback som Redirect URI i Tink Console
+
+python3 -m venv .venv && source .venv/bin/activate
+pip install -r requirements.txt
+uvicorn src.main:app --reload
+# Åbn http://localhost:8000
+```
+
+## Docker
+
+```bash
+docker compose up
+```
+
+## Deploy til i80/Nomad
+
+1. Konfigurer Gitea secrets: `REGISTRY_USER`, `REGISTRY_TOKEN`, `NOMAD_ADDR`, `NOMAD_TOKEN`
+2. Læg Tink credentials i Nomad/Vault: `secret/moneycapp-tink-demo`
+3. Tilføj `https://tink-demo.i80.dk/callback` som Redirect URI i Tink Console
+4. Push til `main` → Gitea Actions bygger og deployer
+
+## Tink Console setup
+
+1. Gå til [console.tink.com](https://console.tink.com)
+2. Opret en app → kopiér Client ID + Secret til `.env`
+3. Under **Redirect URIs**: tilføj din callback URL
+4. Under **Scopes**: aktiver `accounts:read`, `transactions:read`, `credentials:read/write`, `user:create`