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.

server/providers/cctv/quebec.js

@@ -5,6 +5,16 @@ import { cameraDisplayCode, fallbackHeadingFromId } from './normalize.js';
 const QUEBEC_CATALOG_PATH = 'public/quebec-cameras.json';
 export const QUEBEC_CAMERA_SOURCE_COUNT = 1120;
 
+/**
+ * Whether the operator opted in to the browser-direct Québec 511 video. Off by
+ * default: the camera locations are CC BY 4.0, but whether Québec 511's
+ * service terms allow another site to embed its clips is unconfirmed, so an
+ * unset flag lists the cameras with a link to the 511 viewer page only.
+ */
+export function quebecBrowserVideoEnabled(env = process.env) {
+  return String(env.CCTV_QUEBEC_VIDEO_ENABLED || '').trim() === '1';
+}
+
 /** Build the direct browser-only MP4 URL for one namespaced MTQ camera id. */
 export function quebec511VideoUrl(cameraId) {
   const match = /^qc-511-(\d+)$/.exec(String(cameraId || ''));
@@ -99,8 +109,9 @@ export function loadQuebecSources({ sourceRoot = process.cwd() } = {}) {
       mountHeightM: 8,
       groundElevationM: 0,
       feedType: 'image',
-      // No frame URL is registered: 511 denies the server-side media proxy,
-      // while the browser can play its MP4 in the dedicated DOM overlay.
+      // No frame URL is registered: the server never fetches 511 media. With
+      // CCTV_QUEBEC_VIDEO_ENABLED=1 the browser plays the 511 MP4 in the DOM
+      // overlay after a play click; otherwise the camera links to 511.
       url: '',
       snapshotUrl: '',
       sourceKind,
@@ -110,12 +121,12 @@ export function loadQuebecSources({ sourceRoot = process.cwd() } = {}) {
         : null,
       positionSource: String(camera.positionSource || ''),
       license: isTraffic
-        ? 'Données Québec / MTQ, CC BY 4.0'
+        ? 'Locations: Données Québec / MTQ, CC BY 4.0. Video: hosted by Québec 511 under its terms of use'
         : isMontreal
           ? 'OpenStreetMap contributors, ODbL 1.0'
           : 'Operator terms apply; location provenance shown per camera',
       credit: isTraffic
-        ? 'MTQ · CC BY 4.0'
+        ? 'Locations: MTQ · CC BY 4.0 · Video: Québec 511'
         : isMontreal
           ? 'OpenStreetMap contributors · ODbL'
           : provider,