fix(cctv): space out failed background refreshes; test the stale paths

- A background catalog refresh that rejects now keeps the old catalog for
  another TTL, as an empty refresh already did, so a refresh that keeps
  failing is retried once per TTL instead of on every request.
- Trim notes are keyed by the source list they describe, and /sources asks
  for the list it served, so a request answered during a refresh never pairs
  the old cameras with the new list's notes.
- Tests: a failed background refresh (one warning, no unhandled rejection,
  no retry before the TTL, trim notes stay with their list) and an empty
  background refresh (old catalog kept, no upstream fetch before the TTL).
  The race assertion's message now names the failure; its timer is cleared.
- The Tarktee test no longer imports the new constant, so on main it fails
  on its own assertion instead of taking the whole file down.
- precompute-cctv-heights waits 60 s for a cold catalog, past Tarktee's 30 s.
- CURRENT-STATE notes the 30 s bound and the retry spacing.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -4412,7 +4412,9 @@ silently demoting every later lookup for the session.
   ~1,100 cameras total, all RAW PRIOR poses, stills-first. The catalog lives for 15 minutes; once
   it expires, `/api/cctv` keeps answering from it while one background refresh reloads every
   pack, so only the very first load waits for the slowest pack (a live first load took about
-  22 s). Estonia's Tarktee DATEX feeds, which answer in 2 to 16.6 s, get 30 s
+  22 s, and is bounded by Tarktee's 30 s). A background refresh that fails or comes back
+  empty keeps the old catalog and is retried after another 15 minutes, not on the next
+  request. Estonia's Tarktee DATEX feeds, which answer in 2 to 16.6 s, get 30 s
   (`TARKTEE_FETCH_TIMEOUT_MS`) where other packs get 15 s.
 - **CCTV v3 UX — viewshed + calibration gizmo** (built 2026-07-05 and field
   validated 2026-07-21): the COVERAGE toggle is a