Scan floating IPs in the background, page by page, so thousands of addresses work

The "Scan Floating IP" button failed with a client timeout: the project now
holds ~6.4k floating IPs and the scan listed them all in one unpaginated,
timeout-less Neutron request on the HTTP request context.

openstack: ListFreeFloatingIPs reads marker-based pages (fields= keeps them
small) with per-page retry/backoff on transport errors, 5xx and 429, and every
request now has a timeout (also ends hangs inside the orchestrator tick).

orchestrator: the scan is a single-flight background job on the process
context with progress (clearing/listing/enqueuing/done/error), dry_run, full
discovery before anything is enqueued, then SubmitIPs in chunks of 500 in
ascending IP order; a failed read leaves the queue untouched. The auto-cycle
gets a "scanning" phase that polls the job, so the control loop and
autoCycleMu are never held across OpenStack/DB work; it recovers after a
restart and waits for (instead of adopting) a scan started by someone else.

db: migration 0009 (indexes), paged ListIPsPage/ListRegistryPage, GROUP BY
counters, EXISTS completion check, set-based ClearAllIPs.

API: POST /admin/ips/scan -> 202 (dry_run, wait), GET /admin/ips/scan, paging
and filters on /admin/ips and /admin/registry (bare arrays without limit),
results_by_overall in /admin/status.

dashboard: scan progress panel and dry-run button, paginated /ips and
/registry with server-side filters, Overview on counters and capped lists
with progress/ETA, "select all N by filter", hx-params fix for per-row
buttons, real counts in confirmations.

Also: docs (API, USAGE, DASHBOARD, README), plan and review under
docs/changes/, bin/ rebuilt with new SHA256SUMS.

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

internal/dashboard/templates/overview.html

@@ -50,8 +50,8 @@
 </select>
 </div>
 </div>
-<p class="muted" style="padding:0 16px 12px">Действует на обе таблицы ниже. Фильтр по статусу — это фильтр по
-итоговому результату, поэтому при выборе конкретного статуса строки «Текущей проверки» (у неё ещё нет результата)
+<p class="muted" style="padding:0 16px 12px">Действует на все списки ниже. Фильтр по статусу — это фильтр по
+итоговому результату, поэтому при выборе конкретного статуса строки «В работе» и «В очереди» (у них ещё нет результата)
 не показываются.</p>
 </form>