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.

README.md

@@ -435,7 +435,7 @@ Twenty layers and map sources. **Eighteen have a keyless path.** Some offer addi
 | 🌍 **Earthquakes**          | Global seismic activity, last 24h                                                                                                                                                                                                                                                                                                                                                   | USGS                                    | 🟢                                                                                                  |
 | ◍ **Air quality**           | Live AQHI on the published 1–10+ health-risk scale, with a Weather-panel card showing the band legend and the highest readings in view. **Canada only** — ECCC is the first registered provider | ECCC MSC GeoMet                          | 🟢                                                                                                  |
 | 🚗 **Traffic**              | Simulated vehicles on OSM roads. With TomTom, live flow speeds drive the simulation and congestion colors below ~8 km; individual vehicle positions are not live observations                                                                                                                                                                                                       | TomTom + OSM                            | 🟢 simulation · 🟡 live flow speeds                                                                 |
-| 📹 **CCTV Mesh**            | ~7,516 camera locations (4,000 shared slots + 1,120 Québec + 2,396 World image feeds) projected _into_ the 3D space — Austin · Texas (TxDOT) · California (Caltrans) · London (TfL) · Ontario (511, free developer key) · Finland (Fintraffic) · British Columbia (DriveBC) · Estonia (Tallinn, Tarktee) · Delaware (DelDOT live video) · New South Wales (Live Traffic NSW) · Calgary · Norway (Statens vegvesen) · Toronto · King County (WA) · Washington (WSDOT) · Catalonia (Servei Català de Trànsit) · Hong Kong (Transport Department) · Taiwan (Freeway Bureau, MOTC) · Québec (MTQ browser MP4, Montréal locations, regional webcams) · Iceland (Vegagerðin) · Oregon (TripCheck) · Japan (MLIT river cameras) · Italy (A22 Brennero motorway), plus opt-in New York City (NYC DOT TMC, needs your own NYC DOT agreement), opt-in Lithuania (Via Lietuva / Eismoinfo, photo licence unconfirmed) and opt-in Florida (FL511, individual personal use only; other use needs FDOT's written consent). Positions are published or attributed; poses are estimated priors **you calibrate by dragging a gizmo on the camera itself** | City APIs                               | 🟢                                                                                                  |
+| 📹 **CCTV Mesh**            | up to 7,516 camera locations (4,000 shared round-robin slots, plus room for 1,120 Québec and 2,396 World image cameras) projected _into_ the 3D space — Austin · Texas (TxDOT) · California (Caltrans) · London (TfL) · Ontario (511, free developer key) · Ottawa (City of Ottawa, free access certificate) · Finland (Fintraffic) · British Columbia (DriveBC) · Estonia (Tallinn, Tarktee) · Delaware (DelDOT live video) · New South Wales (Live Traffic NSW) · Calgary · Norway (Statens vegvesen) · Toronto · King County (WA) · Washington (WSDOT) · Catalonia (Servei Català de Trànsit) · Hong Kong (Transport Department) · Taiwan (Freeway Bureau, MOTC) · Québec (MTQ locations with Québec 511 links, Montréal locations, regional webcams) · Iceland (Vegagerðin) · Oregon (TripCheck) · Japan (MLIT river cameras) · Italy (A22 Brennero motorway), plus opt-in New York City (NYC DOT TMC, needs your own NYC DOT agreement), opt-in Lithuania (Via Lietuva / Eismoinfo, photo licence unconfirmed), opt-in Québec 511 in-browser video (embedding terms unconfirmed) and opt-in Florida (FL511, individual personal use only; other use needs FDOT's written consent). Positions are published or attributed; poses are estimated priors **you calibrate by dragging a gizmo on the camera itself** | City APIs                               | 🟢                                                                                                  |
 | 📷 **Mapped ALPR Cameras**  | License-plate-reader camera locations tagged by OpenStreetMap contributors, loaded one city-sized view at a time, with **SHOW NEAREST**. Locations and tags only: no plate data, no video                                                                                                                                                                                           | OpenStreetMap (incl. DeFlock mapping)   | 🟢                                                                                                  |
 | 📷 **Street Level**         | Street-level photos behind one panel, one chip per provider: coverage on the streets, image cones, an embedded viewer with full-screen **EXPAND**. Mapillary, Google Street View, KartaView and Panoramax | Mapillary · Google · KartaView · Panoramax | 🟢 KartaView, Panoramax · 🟡 Mapillary token · 🔴 Google Maps key |
 | 📻 **Radio**                | Geolocated world radio with an **analog tuner** — drag the needle across up to 750 stations and the globe flies to each broadcaster                                                                                                                                                                                                                                                 | Radio Browser / broadcasters            | 🟢                                                                                                  |