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>

moneycapp-tink-demo.nomad

@@ -0,0 +1,41 @@
+job "moneycapp-tink-demo" {
+  datacenters = ["dc1"]
+  type        = "service"
+
+  group "demo" {
+    count = 1
+
+    network {
+      port "http" { to = 8000 }
+    }
+
+    service {
+      name = "moneycapp-tink-demo"
+      port = "http"
+      tags = ["traefik.enable=true",
+              "traefik.http.routers.tink-demo.rule=Host(`tink-demo.i80.dk`)",
+              "traefik.http.routers.tink-demo.tls=true",
+              "traefik.http.routers.tink-demo.tls.certresolver=le"]
+      check {
+        type     = "http"
+        path     = "/"
+        interval = "30s"
+        timeout  = "5s"
+      }
+    }
+
+    task "app" {
+      driver = "docker"
+
+      config {
+        image = "registry.i80.dk/gitea/moneycapp-tink-demo:latest"
+        ports = ["http"]
+      }
+
+      resources {
+        cpu    = 256
+        memory = 256
+      }
+    }
+  }
+}