fix: customer-facing cleanup — remove internal branding, print→logging, dynamic dates, sandbox note, next steps

- main.py: neutral API description (remove 'sales demo')
- base.html: 'Open Banking Demo' nav, neutral footer
- demo.py: /debug-session gated behind DEMO_MODE, all print() → logging,
  webhook receiver has C# signature verification example + Tink docs link,
  removed duplicate import
- demo_data.py: all hardcoded 2026 dates replaced with dynamic date helpers
- step2.html: external_user_id terminology (remove tink_external_ref)
- step.html: sandbox note on Step 3 (anonymous vs production flow)
- step6.html: 'Next Steps' section for C#/.NET implementation

src/templates/step6.html

@@ -223,8 +223,7 @@ async def tink_webhook(request: Request):
     Fra brugeroprettelse over live bankdata til real-time webhooks — alt via Tink API.
   </p>
   <p class="text-slate-500 text-sm mb-6 max-w-xl mx-auto">
-    Auth → bruger → bank-tilslutning → konti (v2) → transaktioner (v2) → webhooks. 
-    Et komplet Tink-flow — klar til at blive bygget ind i jeres platform.
+    Auth → bruger → bank-tilslutning → konti (v2) → transaktioner (v2) → webhooks.
   </p>
   <div class="flex gap-3 justify-center flex-wrap">
     <a href="/demo/reset" class="px-5 py-2.5 border border-slate-600 text-slate-300 hover:text-white hover:border-slate-400 rounded-xl text-sm transition">↺ Kør demo igen</a>
@@ -235,6 +234,33 @@ async def tink_webhook(request: Request):
   </div>
 </div>
 
+<!-- Next Steps for implementation -->
+<div class="mt-6 bg-slate-900/60 border border-slate-800 rounded-2xl p-7">
+  <h4 class="text-white font-semibold text-base mb-4 flex items-center gap-2">
+    <svg class="w-4 h-4 text-violet-400" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2"/></svg>
+    Næste skridt mod en produktion-klar integration
+  </h4>
+  <div class="grid md:grid-cols-2 gap-3 text-sm text-slate-400">
+    <div class="bg-slate-800/60 rounded-lg p-4 space-y-1.5">
+      <p class="text-violet-300 font-semibold text-xs uppercase tracking-wider mb-2">Backend (C# / .NET)</p>
+      <p>1. Lav en <code class="text-violet-300 font-mono text-xs">TinkApiClient</code> wrapper (brug <code class="text-xs font-mono">tink/client.py</code> som reference)</p>
+      <p>2. Gem <code class="text-violet-300 font-mono text-xs">external_user_id</code> + <code class="text-violet-300 font-mono text-xs">user_id</code> i din kundedatabase</p>
+      <p>3. Implementér <code class="text-violet-300 font-mono text-xs">/callback</code> endpoint med token exchange</p>
+      <p>4. Gem tokens sikkert (encrypted, server-side — ikke i cookie)</p>
+    </div>
+    <div class="bg-slate-800/60 rounded-lg p-4 space-y-1.5">
+      <p class="text-violet-300 font-semibold text-xs uppercase tracking-wider mb-2">Webhooks & Production</p>
+      <p>5. Byg webhook receiver med <a href="https://docs.tink.com/api#webhook/webhook-endpoints" target="_blank" class="text-violet-400 hover:text-violet-300 underline">HMAC-SHA256 signature verification</a></p>
+      <p>6. Skift til production Tink-credentials (Tink Console)</p>
+      <p>7. Registrér din production callback URI i Tink Console</p>
+      <p>8. Brug <code class="text-violet-300 font-mono text-xs">authorization-grant/delegate</code> i prod-flowet (ikke anon)</p>
+    </div>
+  </div>
+  <p class="text-xs text-slate-600 mt-4">
+    Kildekoden til dette demo (<code class="font-mono">src/tink/client.py</code> og <code class="font-mono">src/routes/demo.py</code>) er skrevet for at være letlæselig og direkte overførbar til andre platforme.
+  </p>
+</div>
+
 <!-- Navigation -->
 <div class="mt-4 flex justify-start">
   <a href="/demo/step/5"