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>

Makefile

@@ -0,0 +1,50 @@
+.PHONY: install run dev docker-build docker-up docker-down push deploy logs vault-setup test clean
+
+REGISTRY = registry.i80.dk
+IMAGE    = $(REGISTRY)/moneycapp-tink-demo
+
+install:
+	python3 -m venv .venv && .venv/bin/pip install -q -r requirements.txt
+	cp -n .env.example .env || true
+	@echo "✓ Done — edit .env with your Tink credentials"
+
+run:
+	.venv/bin/uvicorn src.main:app --host 0.0.0.0 --port 8000
+
+dev:
+	.venv/bin/uvicorn src.main:app --host 0.0.0.0 --port 8000 --reload
+
+docker-build:
+	docker build -t moneycapp-tink-demo .
+
+docker-up:
+	docker compose up
+
+docker-down:
+	docker compose down
+
+# --- Deploy to i80.dk ---
+
+push:
+	docker build --platform linux/amd64 -t $(IMAGE):latest .
+	docker push $(IMAGE):latest
+	@echo "✓ Image pushed to $(IMAGE):latest"
+
+vault-setup:
+	@echo "Storing Tink credentials in Vault..."
+	vault kv put secret/moneycapp-tink-demo \
+		client_id=$(TINK_CLIENT_ID) \
+		client_secret=$(TINK_CLIENT_SECRET) \
+		session_secret=$$(openssl rand -hex 32)
+	@echo "✓ Vault secret stored at secret/moneycapp-tink-demo"
+
+deploy: push
+	scp moneycapp-tink-demo.nomad autobox.i80.dk:/tmp/
+	ssh autobox.i80.dk 'export NOMAD_ADDR=https://nomad.i80.dk:4646 && nomad job run /tmp/moneycapp-tink-demo.nomad'
+	@echo "✓ Deployed — https://tink-demo.i80.dk"
+
+logs:
+	ssh autobox.i80.dk 'export NOMAD_ADDR=https://nomad.i80.dk:4646 && nomad alloc logs -job moneycapp-tink-demo'
+
+clean:
+	rm -rf .venv __pycache__ src/__pycache__ src/**/__pycache__