fix(tiles): derive the tile origin from the configured TileJSON (#933)

`createVectorTileSource` took `tileJsonUrl` and `allowedOrigin` as independent
options, and `createOpenFreeMapSource` hardcoded both to the default host. A
caller that repointed only `tileJsonUrl` — the obvious single change — kept the
default `allowedOrigin`, so the TileJSON's absolute upstream `tiles[0]` passed
the origin check and every tile was fetched from the default host instead. No
error, no warning, and nothing reached the configured mirror.

`allowedOrigin` now defaults to the origin of `tileJsonUrl`, so repointing one
option is enough, and a mirror that serves the default host's TileJSON verbatim
fails with the existing `Invalid vector tile origin` instead of silently
bypassing itself. The origin check is unchanged: a TileJSON still cannot point
the client at a host the caller did not configure.

All three existing callers pass `allowedOrigin` explicitly
(`openFreeMap.js`, `alpr/source.js`, `traffic/flowSource.js`), and an explicit
value still overrides the derived one, so behaviour is unchanged for every
current call site.

src/sources/openFreeMap.js

@@ -214,11 +214,18 @@ function decodeLayers(bytes, z, x, y, layerNames) {
   return { roads, military };
 }
 
-/** Construct an immutable-version road/military tile source without starting I/O. */
+/**
+ * Construct an immutable-version road/military tile source without starting I/O.
+ *
+ * `allowedOrigin` is deliberately not set here: `createVectorTileSource`
+ * derives it from whichever `tileJsonUrl` is in effect, so a caller that
+ * repoints only `tileJsonUrl` gets tiles from that host or a named error —
+ * never a silent fall back to the default host (#933). Passing
+ * `allowedOrigin` explicitly still overrides both.
+ */
 export function createOpenFreeMapSource(options = {}) {
   return createVectorTileSource({
     tileJsonUrl: 'https://tiles.openfreemap.org/planet',
-    allowedOrigin: 'https://tiles.openfreemap.org',
     decode: decodeOpenFreeMapTile,
     maxEntries: 192,
     maxCacheBytes: 64 * 1024 * 1024,