Scrape the official alarm level thresholds (Richtwasserstände) from the
station detail page and include them in GET /api/pegel/{pegel_id} as
alarm_thresholds, cached for 24 hours with a stale-cache fallback on
errors. null for stations without a flood alert function.
Also clarify in the flood_alert_level docs that 'Kein Hochwassermeldepegel'
means the station is not used for official flood alerts/control, not
that measurement data is missing.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
The source sometimes returns placeholder entries (no water level, no flow) for the newest timestamps. Skip them so latest is the most recent entry with real data.
