feat(geocoder): derive geocoderProvider from Poracle's remote config - #1244

Stacked on #1243. Base is fix/geocoder-photon-misconfig so the shared test file does not conflict; retarget to main once that merges.

Requires the PoracleNG side, which adds provider to the /api/config/poracleWeb payload.

The asymmetry this removes

nominatimUrl already falls back to Poracle's providerURL, so a deployment can take its geocoder URL from Poracle and never mention it in ReactMap's config. The backend type had no such fallback:

if (providerURL && !this.nominatimUrl) this.nominatimUrl = providerURL   // derived
// geocoderProvider — local config only

Half the pair auto-populated and the other half did not. An operator whose URL came from Poracle still had to hand-set geocoderProvider locally, and if they did not, every request silently took the Nominatim branch against a Photon URL. That is not a hypothetical: it is what took a production instance down after #1242 shipped.

PoracleNG now reports the backend behind providerURL as provider, so geocoderProvider can follow the same rule as its URL. Local config still wins, matching how providerURL and addressFormat already behave.

Ignored backends

Poracle also offers google and none. Neither has a ReactMap equivalent, so they resolve to undefined rather than being mapped onto nominatim, which would claim something untrue about the backend. The match is exact, so a differently-cased value is ignored rather than guessed at.

The name collision

provider is destructured out of remoteConfig whether or not it is usable:

const { providerURL, provider, addressFormat, ...rest } = remoteConfig
Object.assign(this, rest)

this.provider is the webhook provider, set from webhook.provider in the constructor. It is an unrelated field that happens to share a name with Poracle's geocoding provider, and letting the remote value through the spread would silently overwrite it. It is currently read nowhere else in ReactMap, so this would have been invisible until something started reading it.

Testing

The resolution lives in a small exported function because #fetchConfig is private and would otherwise need a stubbed HTTP round trip to reach.

Four cases: the derivation, local precedence over the remote value, the ignored backends, and the webhook provider surviving a remote payload that carries a geocoding provider.

• yarn lint passes
• yarn build passes
• yarn prettier passes
• node --test server/test/geocoder.test.js passes 30/30

Not exercised against a live Poracle. The payload shape is taken from PoracleNG's poracleWebResponse struct and its OpenAPI golden, not from a real response, so the field name is worth confirming against a running instance before merge.

yarn test also runs server/test/rocketPokemonFiltering.test.js, which fails with No database selected for React Map Tables. Unrelated and predates this branch: server/src/db/knexfile.cjs calls process.exit(9) at import when no schema has user in its useFor.