Merge upstream/main: KartaView provider meets i18n

Upstream's KartaView PR (#1121) extracted the Mapillary coverage engine
into a shared lineCoverage.js and made the panel wording
provider-specific (coverage noun/action, SINCE upload-date note,
highlightsSequence legend gate), again in the regions this branch
localizes.

- mapillary/coverage.js: taken as upstream's thin re-export of the new
  lineCoverage.js; the generic too-high hint stays msg()-marked, now in
  lineCoverage.js where the default lives.
- kartaview/policy.js: coverage hints (tooHigh, noCoverage) marked as
  msg() data so they translate like every other coverage hint; thrown
  error messages stay English, matching the Mapillary precedent.
- presentMeta: KartaView counts streets, and Russian plurals need the
  noun inside the template, so the count line gets its own literal tn
  pair keyed off coverageLabel.noun, falling back to the sequences pair;
  upstream's noun/action data contract is untouched.
- uiState legend: upstream highlightsSequence gate with t('Selected');
  sinceNote localized with a {names} placeholder.
- layer-panels.html: sl-since-note wiring kept, data-i18n hooks kept.
- CHANGELOG: both sides kept. es/ru: 4 new keys each.

npm run i18n complete (953 messages each); npm test 6504/6506 (the one
failure is the pre-existing environmental OPENAI_API_KEY leak in
devFreshDotenv, unrelated); build passes.

CHANGELOG.md

@@ -1,5 +1,16 @@
 # Changelog
 
+- Add New York City traffic cameras from the NYC DOT Traffic Management Center
+  as an opt-in CCTV pack. NYC DOT requires a data-sharing agreement for the
+  camera feed, so the pack is off unless `CCTV_NYC_ENABLED=1` is set by an
+  operator who holds one; otherwise no request reaches NYC DOT. NYC DOT's
+  requested disclaimer is in the Data attribution popover. The camera list is one keyless JSON request to
+  `webcams.nyctmc.org/api/cameras`; frames are stills synthesized from each
+  camera UUID on that same host, so a catalog field cannot steer the proxy
+  off-host. Offline cameras are dropped. Once enabled, the 250 cameras nearest
+  the five borough cores load and `CCTV_NYC_MAX_SOURCES` changes the cap. The catalog-wide ceiling is
+  unchanged; extra cameras share it round-robin with the other packs.
+
 - Spanish interface (`es`), translated by @meirm (#602) and reviewed against the
   current English.
 
@@ -107,6 +118,29 @@
 
 ## [Unreleased]
 
+- Street Level: KartaView is the third provider, keyless. Light its chip
+  (purple; off by default, one provider at a time) and zoom in below about
+  6 km: the lines are the streets KartaView has photos of (z13–14 tiles from
+  `api.kartaview.org`). A click on a line opens the photo nearest the click
+  without moving the camera, flat or 360° (a small WebGL panorama: drag to
+  look, wheel to zoom), with cones along its drive and ‹ › / ← → to step
+  through it. The caption links to the full-size photo (KartaView's photo
+  pages fail for signed-out visitors), and the globe credits "© KartaView
+  contributors, CC BY-SA 4.0". Share links carry it in the provider
+  switches (`0.m.0_0.r.google-0*kartaview-1`). Archived photos (KartaView
+  answers 409) are skipped by the click and by ‹ ›. Shift+← →, ↑ ↓, + − and
+  pinch look around a 360° photo. The open photo's marker is a purple view
+  cone pointing along the drive (KartaView's own compass headings are often
+  0 or far off). The IMAGERY (ALL / 360° / FLAT) and SINCE filters apply to
+  KartaView as to Mapillary: its lines are filtered by KartaView's own
+  server (its filtered PNG tiles, as a mask over the JSON lines), and the
+  photo a click opens, and the cones, by each photo's projection and upload
+  date. KartaView's SINCE is the upload date (all its server can filter by);
+  a note under the slider says so while KartaView is lit (`sinceBasis:
+  'upload'` in the provider contract).
+  Mapillary's line coverage and sequence cones are now shared by both
+  (`lineCoverage.js`, `sequenceCones.js`).
+
 - Street Level: Google Street View is the second provider. On the Google 3D
   map (Google's terms keep it off other maps), light its chip (off by
   default: every panorama is billed to the Google Maps key, which needs the