build: ship each bundled data pack once

loadBundledJson's callers passed a literal JSON import as a Node fallback,
which made the production build emit a JavaScript copy of every pack beside
the JSON the browser fetches. The loader now reads file: URLs itself under
Node (through process.getBuiltinModule, synchronously, as promptly as the
cached import it replaces), and the callers pass only the URL. On a Node too
old to provide getBuiltinModule it says that Node 24.14 or newer is needed.
dist/ drops from 54 MB to 42 MB. A test keeps app code from importing a pack
as a module.

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

src/data/militaryNames.js

@@ -14,10 +14,6 @@ export function createMilitaryNamesLoader({
   loadPack = (signal) =>
     loadBundledJson(
       new URL('./local_data/osm_military_names/names.json', import.meta.url),
-      () =>
-        import('./local_data/osm_military_names/names.json', {
-          with: { type: 'json' },
-        }),
       { signal },
     ),
   timeoutMs = MILITARY_NAMES_TIMEOUT_MS,