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>

Dockerfile

@@ -0,0 +1,13 @@
+FROM python:3.12-slim AS base
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY src/ src/
+COPY .env.production .env
+
+EXPOSE 8000
+
+CMD ["uvicorn", "src.main:app", "--host", "0.0.0.0", "--port", "8000"]