Watch EPIRent version and archive its download packages

- Poll the public download page for "Aktuelle Version <nr> vom <date>",
  report changes through the normal change feed and notification mail,
  and show the current version as a card on the overview. Runs on its own
  interval (default 30 min); the first run only records a baseline.
- Archive epirentServer.zip / epirentClient.zip per version number so we
  keep a download cache and history: streamed to disk with SHA-256 and
  size, fetched in a background thread so ticket polling is unaffected,
  with a free-space check before downloading (~1.1 GB per version).
- Retention is configurable via EPIRENT_DOWNLOAD_KEEP, where 0 means
  unlimited; a successful archive is reported as a change and by mail.
- New Downloads page listing the archived versions with checksums and
  links to fetch the cached files.
- Notification lines now omit the arrow when there is no previous value
  and drop the "#" for entries without a ticket.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/notify.py

@@ -22,18 +22,23 @@ def send_change_mail(changes: list[dict]) -> None:
 
     lines = []
     for c in changes:
-        line = f"#{c['ticket_number']}  {c['ticket_title']}\n    {c['label']}: {c.get('old_value') or '–'} -> {c.get('new_value') or '–'}"
+        # Einträge ohne Ticketbezug (z. B. EPIRent-Version) ohne "#" ausgeben
+        head = f"#{c['ticket_number']}  " if c.get("ticket_number") else ""
+        new = c.get("new_value") or "–"
+        # ohne Vorwert (z. B. neues Ticket, Download-Archiv) keinen Pfeil setzen
+        value = f"{c['old_value']} -> {new}" if c.get("old_value") else new
+        line = f"{head}{c['ticket_title']}\n    {c['label']}: {value}"
         if c.get("detail"):
             line += f"\n    {c['detail']}"
         lines.append(line)
     body = (
-        f"Es gibt {len(changes)} neue Änderung(en) an euren EPI-Support-Tickets:\n\n"
+        f"Es gibt {len(changes)} neue Änderung(en):\n\n"
         + "\n\n".join(lines)
         + f"\n\nDashboard: {config.ZAMMAD_URL}\n(Quelle: EPI-Support-Monitor)"
     )
 
     msg = EmailMessage()
-    msg["Subject"] = f"[EPI-Support] {len(changes)} Ticket-Änderung(en)"
+    msg["Subject"] = f"[EPI-Support] {len(changes)} Änderung(en)"
     msg["From"] = config.SMTP_FROM
     msg["To"] = ", ".join(config.NOTIFY_TO)
     msg.set_content(body)