Merge upstream/main into pr/mapillary-layer

Brings in #744 (share-link token ledger). package.json: keep the branch's
sorted scripts and add layer-token:next and layer-token:check.

Street Level's token moves from the provisional `3` to `0`: following
CONTRIBUTING, the provisional entry was removed and
`npm run layer-token:next -- street-level` assigned `0` (free digits in
order). It is added to the registry and to
src/data/layerStateTokenReservations.json, and
`npm run layer-token:check -- --base-ref upstream/main` passes (28
published, 1 new). No link with the provisional token was ever published.

Pinned token tests move with the ledger as CONTRIBUTING asks: 29
reservations, next free digit `3`, and the competing-PR and retired-digit
scenarios shift up one free digit (0->3, 3->4) so they still test the same
rules. The README share examples and the free-digit notes in
CONTRIBUTING and CURRENT-STATE now read `0`.

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

CHANGELOG.md

@@ -63,6 +63,19 @@
   `src/app/atmosphereCompat.test.mjs` pins the probe, the platform matrix and
   the `renderable`-not-`enabled` choice (KnottyDyes, #705).
 
+- Make share-link layer tokens durable allocations instead of ad hoc picks.
+  Existing one-character mappings are pinned permanently, while new layers use
+  the next free single-character digit, then two-character base-36 tokens.
+  Authors record each token in the permanent JSON ledger after running
+  `npm run layer-token:next -- <layer-id>` on a rebased branch.
+  `npm run layer-token:check -- --base-ref origin/main` guards published
+  assignments and allocation order in
+  pull-request CI. Existing v2 links keep their exact meaning.
+  Malformed enabled-layer lists now reject the whole layer payload instead of
+  restoring a partial list. A QA-only browser fixture exercises the future
+  two-character path after a fixture-only exhausted-digit scenario, without
+  reserving `00` in production.
+
 - Region scopes in voice analyst queries ("in the Gulf of Mexico", "over
   the Alps") work again in the dev server: the bundled Natural Earth and
   neighborhood packs are fetched as JSON in the browser