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]>

package.json

@@ -39,6 +39,8 @@
     "doctor": "node scripts/setup-doctor.mjs",
     "format": "node scripts/format.mjs --write",
     "format:check": "node scripts/format.mjs --check",
+    "layer-token:check": "node scripts/check-layer-state-tokens.mjs",
+    "layer-token:next": "node scripts/next-layer-state-token.mjs",
     "opensky:import": "./scripts/opensky-import-client.sh",
     "preview": "vite preview",
     "qa:map-source-tray": "node scripts/qa-map-source-tray.mjs",