feat(frontend): use offline global birth place hierarchy

frontend/src/data/WORLD_LOCATION_DATA.md

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+# World location data
+
+`public/data/world-locations/*.json` is a generated, country-split snapshot used by the profile form. The browser loads the country index first, then loads only the selected country's region/city file. Overseas locations intentionally use cascading selection instead of free-text search.
+
+- Source repository: `dr5hn/countries-states-cities-database`
+- Release: `v3.2-export.7`
+- Upstream export: `json-countries+states+cities.json.gz`
+- License: ODbL-1.0
+- Refresh command: `npm run data:world`
+- Generated: 229 countries, 5,308 regions, 152,970 cities
+
+The generated coordinates are administrative/city-centre coordinates. The source timezone is only a candidate. Before saving a profile, the app still resolves the historical IANA timezone and UTC offset through `/api/locations/timezone`; an unresolved timezone is not saved as a usable location.
+
+Countries without a state/region record in this upstream export are omitted from the selectable index rather than guessed from a search result or fabricated coordinates.

frontend/src/data/world-countries.ts

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+import source from "./world-countries.json";
+
+export type WorldCountry = {
+  code: string;
+  name: string;
+  nativeName?: string;
+  regionCount: number;
+};
+
+export type WorldCountryIndex = {
+  source: {
+    repository: string;
+    release: string;
+    url: string;
+    license: string;
+  };
+  countries: WorldCountry[];
+};
+
+export type WorldCity = {
+  code: string;
+  name: string;
+  nativeName?: string;
+  latitude: number;
+  longitude: number;
+  timezone: string;
+};
+
+export type WorldRegion = {
+  code: string;
+  name: string;
+  nativeName?: string;
+  latitude: number;
+  longitude: number;
+  timezone: string;
+  cities: WorldCity[];
+};
+
+export type WorldCountryData = {
+  code: string;
+  name: string;
+  nativeName?: string;
+  regions: WorldRegion[];
+};
+
+export const worldCountryIndex = source as WorldCountryIndex;
+export const worldCountries = worldCountryIndex.countries;