Show the date a link was added

The created_at timestamp was already stored but never displayed. Add
a "datum" Jinja filter that converts the stored UTC value to local
time and render it on both the link card and the edit form.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/main.py

@@ -1,4 +1,5 @@
 import json
+from datetime import datetime, timezone
 from pathlib import Path
 
 from fastapi import Depends, FastAPI, Form, Request
@@ -26,6 +27,18 @@ templates.env.globals.update(
 )
 
 
+def format_datum(value: datetime | None) -> str:
+    """Formatiere einen UTC-Zeitstempel als lokale Datums-/Zeitangabe."""
+    if not value:
+        return ""
+    if value.tzinfo is None:
+        value = value.replace(tzinfo=timezone.utc)
+    return value.astimezone().strftime("%d.%m.%Y, %H:%M")
+
+
+templates.env.filters["datum"] = format_datum
+
+
 # ---------------------------------------------------------------------------
 # Hilfsfunktionen
 # ---------------------------------------------------------------------------

app/templates/_link_card.html

@@ -6,6 +6,9 @@
       <div class="muted" style="font-size:.8rem; overflow:hidden; text-overflow:ellipsis; white-space:nowrap;">
         {{ link.url }}
       </div>
+      <div class="muted" style="font-size:.75rem; margin-top:3px;">
+        🕓 hinzugefügt am {{ link.created_at | datum }}
+      </div>
     </div>
     <div style="display:flex; gap:4px; flex-shrink:0;">
       <button class="ghost" style="padding:4px 10px; font-size:.8rem;"

app/templates/_link_card_edit.html

@@ -1,9 +1,12 @@
 <div class="panel link-card" id="link-{{ link.id }}">
   <form hx-put="/links/{{ link.id }}" hx-target="#link-{{ link.id }}" hx-swap="outerHTML"
         hx-disabled-elt="button">
-    <div class="muted" style="font-size:.8rem; overflow:hidden; text-overflow:ellipsis; white-space:nowrap; margin-bottom:8px;">
+    <div class="muted" style="font-size:.8rem; overflow:hidden; text-overflow:ellipsis; white-space:nowrap;">
       {{ link.url }}
     </div>
+    <div class="muted" style="font-size:.75rem; margin:3px 0 10px;">
+      🕓 hinzugefügt am {{ link.created_at | datum }}
+    </div>
 
     <div class="field">
       <label>Titel</label>