feat(retention): every growing table is pruned; the audit log has its own window; charts read the raw window from Settings (#5155)

- prune_by_age(column) registers a time-series column with the hourly cleanup;
  Traefik (metrics, access summaries, global stats) and UniFi (WAN, client,
  WLAN, DPI, events, alarms, speedtests) register theirs in setup().
- Alert events join monitor results and Ansible runs on data.retention_days,
  read from Settings each run; Ansible run log files older than it are deleted.
- audit.retention_days (365) keeps the audit log longer, set on Settings > General.
- metric_series.points reads metrics.retention.raw_days, so the chart's
  raw/rollup seam is where the rollup put it (RAW_DAYS removed).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/templates/settings/general.html

@@ -58,7 +58,14 @@
     <label>Data retention <span style="color:var(--text-muted);font-size:0.8rem;">(days)</span></label>
     <input type="number" name="data.retention_days" min="1"
            value="{{ settings['data.retention_days'] }}" style="max-width:120px;">
-    <div style="font-size:0.78rem;color:var(--text-muted);margin-top:0.25rem;">Old ping/DNS results older than this are pruned by the cleanup job.</div>
+    <div style="font-size:0.78rem;color:var(--text-muted);margin-top:0.25rem;">Monitor results, Ansible runs and their logs, alert history, and Traefik and UniFi samples older than this are pruned by the hourly cleanup. Host metrics, Docker data and container logs have their own windows under Settings → Thresholds.</div>
+  </div>
+
+  <div class="form-group">
+    <label>Audit log retention <span style="color:var(--text-muted);font-size:0.8rem;">(days)</span></label>
+    <input type="number" name="audit.retention_days" min="1"
+           value="{{ settings['audit.retention_days'] }}" style="max-width:120px;">
+    <div style="font-size:0.78rem;color:var(--text-muted);margin-top:0.25rem;">Who changed what. Kept longer than operational data; entries older than this are pruned by the hourly cleanup.</div>
   </div>
 
   <div class="form-group">