Merge origin/main: Google Street View, KartaView and Panoramax on the slim Street Level

Main gained three imagery providers (Google Street View, KartaView,
Panoramax), shared line-coverage, cone and photo-viewer modules, one source
lit at a time and the translated interface. Their shared modules still
carried what this branch removes, so the merge ports them onto it:

- lineCoverage.js is this branch's coverage.js made provider-neutral
  (draped lines near the ground only, the selection drawn over them, key
  and rate-limit blocking); sequenceCones.js is sequences.js the same way.
  Mapillary, KartaView and Panoramax all build on them; Mapillary moves
  back to providers/mapillary/ beside the others.
- No ground casting, mesh sampling, surface modes, FOLLOW, legend, prewarm,
  orbit overview points (Panoramax's density dots included), stale-tile
  swaps or water-filled point budget come back.
- Kept from main because the new providers need them: requiresMapStack and
  attachMapStackController (Street View on Google 3D only), ground clicks,
  openNearest with an optional provider nearestImage, openImage {frame},
  reportError, the view-cone marker (now an SVG glyph), filters /
  coverageLabel / sinceBasis, OPEN STREET VIEW, keyAlternatives and i18n.
- photoViewer.js treats the viewer as expanded when its wrap is full screen
  or the iPhone popover, as EXPAND now is.
- The fixture browser gate keeps its 8 steps and adds one each for
  KartaView and Panoramax; catalogs, docs, boundaries and format scope
  follow.

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

CONTRIBUTING.md

@@ -54,8 +54,8 @@ head -40 scripts/qa-radio.mjs  # what this runnable gate proves and how to run i
 Runnable gate entrypoints document what they assert and how to invoke them.
 Most need a dev server; some also need a specific provider key or port. Follow
 the entrypoint's header rather than assuming every matching file accepts the
-same arguments. Only a couple (`qa:map-source-tray`, `qa:transit`) have an
-`npm run` alias.
+same arguments. Four have an `npm run` alias: `qa:map-source-tray`,
+`qa:street-level`, `qa:street-level:fixtures` and `qa:transit`.
 
 If you aren't sure which gate covers your change, search `docs/CURRENT-STATE.md`
 for the feature: it names the gate for many of them, and it's the authoritative
@@ -63,7 +63,7 @@ runtime reference either way. `scripts/qa-l9-matrix.mjs` aggregates the broader
 release-candidate checks and selected harnesses; it does not replace the focused
 gate for the feature you changed.
 
-> **CI does not cover this for you.** The workflow runs the setup policy
+> **CI covers only two of these for you.** The workflow runs the setup policy
 > checks, the formatting and package-boundary checks, the unit suite and the
 > production build, plus a Windows onboarding job. It runs neither
 > `npm run test:track` nor any `qa-*.mjs` gate except the Street Level fixture
@@ -79,8 +79,8 @@ if its layer is later removed.
 
 New layers first use the remaining unreserved single-character digits (`0`
 through `9`), then the two-character base-36 namespace (`00` through `zz`). On the
-current published ledger, `0`, `1` and `2` are already owned, so the next
-choices are `3` through `9`, then `00`. After rebasing onto the latest `main`, run
+current published ledger, `0`, `1`, `2` and `3` are already owned, so the next
+choices are `4` through `9`, then `00`. After rebasing onto the latest `main`, run
 `npm run layer-token:next -- <layer-id>`, add that result to both the permanent
 JSON reservation ledger and registry entry, and keep the exact registered-layer
 count assertion up to date. The token is assigned against the merge-time base, not
@@ -98,7 +98,7 @@ remove only your still-unpublished layer's registry entry and ledger row so the
 local registry is valid again, then rerun `npm run layer-token:next -- <layer-id>`.
 For example, if PR A publishes `0` while PR B still provisionally uses `0`,
 PR B removes only its own provisional entry, reruns the helper, and receives
-`3`. Put `3` on PR B's registry entry and ledger row, update its pinned count
+`4`. Put `4` on PR B's registry entry and ledger row, update its pinned count
 and token tests, then rerun `npm run layer-token:check -- --base-ref origin/main`.
 An invalid duplicate ledger can fail during module import before the helper
 prints anything; never fix that by renaming or deleting PR A's published token.
@@ -126,6 +126,7 @@ The highest-leverage places to jump in:
 - ES modules, **2-space indent, single quotes, semicolons.**
 - JSDoc on exported/public functions.
 - Match the surrounding code — comment density, naming, and idiom.
+- User-visible text goes through `t()`, `tn()` or `msg()`, or a `data-i18n*` attribute in markup, and `npm run i18n` must pass. See [docs/I18N.md](docs/I18N.md).
 - Prefer small, reviewable commits. Conventional-commit-style prefixes (`feat:`, `fix:`, `perf:`, `docs:`) are appreciated but not required.
 
 ## Formatting and reusable components
@@ -149,7 +150,7 @@ ownership and adoption process.
 
 1. Branch off `main`.
 2. Keep `npm run build`, `npm test`, and `npm run test:track` green and avoid new console errors, plus the [feature gate](#feature-regression-gates) for the area you touched.
-3. If you change runtime behavior, update `docs/CURRENT-STATE.md` and `CHANGELOG.md` in the same PR.
+3. If you change runtime behavior, update `docs/CURRENT-STATE.md` in the same PR, and add your changelog entry as `changelog.d/<pr-number>-<slug>.md` instead of editing `CHANGELOG.md` — see [changelog.d/README.md](changelog.d/README.md). Distinct filenames don't conflict; a release assembles the directory into `CHANGELOG.md`. A documentation claim that needs a regression test should assert against `docs/CURRENT-STATE.md` or `README.md`, which a PR still edits directly.
 4. If you add or change a data source, update [DATA_SOURCES.md](DATA_SOURCES.md) with its license and attribution. **Don't add data you don't have the right to redistribute** — fetch it at runtime instead.
 5. Describe what you changed and how you verified it (screenshots welcome for anything visual).