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>

bin/SHA256SUMS

@@ -1,4 +1,4 @@
-a0eac5409a2929d641ef2a217c31f1b6a974a8679da866ebbb50ff1d5b57df8d  control-api
-5d7fb2f476871843ae4179dddb61e77d3f71e8eb73a00e331f0119d8893ba813  validator-agent
-23c687a988350c61f486d400af654bd563865fff59421c437eb679e0e4e10500  prober
-90921ad25f16a922124368770e439d1228c5b0bf7126ba6c726f3fb98bb22f7a  admin-dashboard
+26ff297b66a0c974b7143179e44a58f476265482cd1929bc01a95ad29e50ca7a  control-api
+091ad94b5706b1778b181542de7a4b251cd16c421144269d0955769603d51e06  validator-agent
+3e9e14dbb361ee76aaad7c1da6864b3ea111e0ed151403f904b12485631bbf75  prober
+d72234688eb1954dbff420ca1c8e83b83ceab561b18a0336af0f73fe4d9ac8be  admin-dashboard