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/config.py

@@ -28,6 +28,25 @@ ZAMMAD_PASSWORD = os.getenv("ZAMMAD_PASSWORD", "")
 # --- Abruf ---
 POLL_INTERVAL_SECONDS = int(os.getenv("POLL_INTERVAL_SECONDS", "180"))
 
+# --- EPIRent-Versionsüberwachung (Download-Seite) ---
+EPIRENT_CHECK_ENABLED = _b(os.getenv("EPIRENT_CHECK_ENABLED"), True)
+EPIRENT_URL = os.getenv("EPIRENT_URL", "https://www.epi.rent/downloads")
+EPIRENT_CHECK_INTERVAL_SECONDS = int(
+    os.getenv("EPIRENT_CHECK_INTERVAL_SECONDS", "1800"))
+
+# --- Download-Archiv (pro Version zwischengespeichert) ---
+EPIRENT_DOWNLOAD_ENABLED = _b(os.getenv("EPIRENT_DOWNLOAD_ENABLED"), True)
+EPIRENT_DOWNLOAD_URLS = [
+    u.strip() for u in os.getenv(
+        "EPIRENT_DOWNLOAD_URLS",
+        "https://download.epi.rent/latest/epirentServer.zip,"
+        "https://download.epi.rent/latest/epirentClient.zip"
+    ).split(",") if u.strip()
+]
+# Wie viele Versionsstände aufbewahrt werden (je ~1,1 GB!).
+# 0 = unbegrenzt aufbewahren (es wird nichts automatisch gelöscht).
+EPIRENT_DOWNLOAD_KEEP = int(os.getenv("EPIRENT_DOWNLOAD_KEEP", "3"))
+
 # --- Web ---
 URL_PREFIX = os.getenv("EPISUPPORT_URL_PREFIX", "/episupport").rstrip("/")
 PORT = int(os.getenv("EPISUPPORT_PORT", "8071"))