Restyle link cards as a uniform tile grid

Cards previously had ragged heights because summaries vary in length.
Follow the community-scripts.org card pattern instead: fixed-height
title and summary blocks (clamped to 2 and 3 lines with an ellipsis),
a colored letter avatar derived from the domain, category and
manufacturer as badges in the header, tags in a single clipped row,
and domain plus added-date in a footer.

The avatar color is derived locally from the domain, so no external
favicon requests are made.

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

app/main.py

@@ -1,6 +1,7 @@
 import json
 from datetime import datetime, timezone
 from pathlib import Path
+from urllib.parse import urlparse
 
 from fastapi import Depends, FastAPI, Form, Request
 from fastapi.responses import HTMLResponse, RedirectResponse, Response
@@ -36,7 +37,20 @@ def format_datum(value: datetime | None) -> str:
     return value.astimezone().strftime("%d.%m.%Y, %H:%M")
 
 
+def domain_of(url: str) -> str:
+    """Hostname ohne 'www.' – dient als Kürzel/Beschriftung der Karten."""
+    host = urlparse(url or "").hostname or ""
+    return host[4:] if host.startswith("www.") else host
+
+
+def avatar_hue(url: str) -> int:
+    """Stabile Farbe pro Domain, damit Karten wiedererkennbar sind."""
+    return sum(ord(c) for c in domain_of(url)) % 360
+
+
 templates.env.filters["datum"] = format_datum
+templates.env.filters["domain"] = domain_of
+templates.env.filters["hue"] = avatar_hue
 
 
 # ---------------------------------------------------------------------------