Resolve host IPs through DNS, add purge, French date format by default

- Reverse DNS (cached PTR lookups): IP hosts are stored with their name
  in 'host' and the IP in 'host_ip'; older IP-only logs are resolved on
  display and the host filter shows 'name (IP)'. RDNS / DNS_SERVER env.
- Settings > Danger zone: delete all logs (type PURGE to confirm) through
  VictoriaLogs /delete/run_task; -delete.enable added to docker-compose.
  ALLOW_PURGE env to disable it.
- Remove the custom YYYY-MM-DD - HH:MM:SS:mmm format; default is now the
  usual French display DD/MM/YYYY HH:MM:SS.

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

web/style.css

@@ -332,6 +332,14 @@ select.field:focus { outline: 0; border-color: var(--accent); box-shadow: 0 0 0
   margin: 10px 0 6px !important; padding: 8px 12px; border-radius: 8px;
   background: var(--panel-2); font-family: var(--mono); font-size: 12.5px;
 }
+.set-section.danger h3 { color: var(--sev-err); }
+.purge-row { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin-top: 10px; }
+.btn.danger { color: var(--sev-err); border-color: color-mix(in srgb, var(--sev-err) 45%, var(--border)); }
+.btn.danger:hover:not(:disabled) { background: var(--sev-err); border-color: var(--sev-err); color: #fff; }
+.btn:disabled { opacity: .5; cursor: not-allowed; }
+.purge-status { font-size: 12.5px; }
+.purge-status.bad { color: var(--sev-err); }
+.purge-status.good { color: var(--sev-info); }
 .set-section footer { display: flex; flex-wrap: wrap; gap: 8px; justify-content: space-between; margin-top: 14px; }
 
 .seg { display: inline-flex; padding: 3px; gap: 3px; background: var(--panel-2); border: 1px solid var(--border); border-radius: 10px; }