fix(cctv): key-gate Ottawa, opt-in Québec video, keep shared slots

Review fixes for #1506.

- Ottawa: use the documented camera list and the city's Traffic Camera
  Images API. The pack is skipped with no request unless
  OTTAWA_CAMERA_CERTIFICATE is set; the certificate is added only at
  fetch time inside the pinned /opendata/ path, and each camera is
  fetched at most once a minute through the shared frame cache.
- Québec 511 video is opt-in (CCTV_QUEBEC_VIDEO_ENABLED=1) and loads
  only after the viewer presses Play; selection, auto-hop, scenes and
  voice no longer contact Québec 511. Credit splits locations (MTQ,
  CC BY 4.0) from video (Québec 511). Interrupted play() is no longer
  reported as an unavailable source; the per-frame listener runs only
  while a Québec camera is selected and the canvas rect is cached.
- Catalog cap: reserved Québec and World slots come only from capacity
  above the 4,000 shared slots, so a lower CCTV_MAX_SOURCES thins every
  pack instead of starving the existing ones. dev-fresh and
  .env.example default to 7,516.
- Throttled frames (World, Ottawa): inside the refresh floor with no
  cached frame the proxy serves the placeholder, never Street View; a
  failed fetch backs off for a minute; the cache is bounded by bytes.
- MJPEG first-frame extraction runs only for sources registered as
  MJPEG (Taiwan Highway Bureau), caps a frame at 2 MB, reads in linear
  time, accepts a CRLF preamble and a boundary that already starts with
  "--", and ends a part without Content-Length at the next delimiter.
  THB hosts are registered in the redirect pin list.
- Tests: World loader policy, Québec loader and opt-in, proxy cooldown
  without Street View, Ottawa signing, cap reservations at 7,516, 4,000
  and 48, overlay Play gate, refresh, visibility and teardown. Guard
  tests check the 4,000 shared slots again.
- Remove the unused standalone Québec preview module and public page.
- Docs: DATA_SOURCES, SECURITY, CURRENT-STATE, CCTV_INTEGRATION, README,
  .env.example, changelog fragment renamed to its full scope.

changelog.d/1506-cctv-taiwan-quebec-ottawa-world.md

@@ -0,0 +1,8 @@
+- Expand CCTV coverage with a keyless Taiwan Highway Bureau fallback, 1,120
+  Québec camera locations, City of Ottawa traffic cameras (needs a free city
+  access certificate, `OTTAWA_CAMERA_CERTIFICATE`), and 2,396 curated
+  image-backed cameras from Iceland, Oregon, and Japan (InoukT, #1506).
+- Québec 511 in-browser video is opt-in (`CCTV_QUEBEC_VIDEO_ENABLED=1`) and
+  loads only after the viewer presses Play; enforce provider-specific frame
+  refresh limits, and report recognized MLIT maintenance images as degraded
+  instead of healthy camera snapshots.

changelog.d/1506-taiwan-highway-cctv-fallback.md

@@ -1,6 +0,0 @@
-- Expand CCTV coverage with a keyless Taiwan Highway Bureau fallback, Québec
-  camera catalog and map preview, Ottawa traffic cameras, and 2,396 curated
-  image-backed cameras from Iceland, Oregon, and Japan (InoukT, #1506).
-- Keep Québec 511 video browser-only, enforce provider-specific frame refresh
-  limits, and report recognized MLIT maintenance images as degraded instead of
-  healthy camera snapshots.