feat: add Railway-ready Jyotish chat product

frontend/src/data/CHINA_LOCATION_DATA.md

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+# China location data
+
+`china-locations.json` is a compact runtime snapshot for the profile form. It contains only the country, province, city, district/county names, administrative codes, and centre coordinates required by the product; it intentionally does not include map polygons.
+
+- Source: ChinaGeoJson `info.json`, which republishes DataV.GeoAtlas administrative metadata.
+- Upstream license: MIT (ChinaGeoJson, Copyright 2024 ChuXiao).
+- Refresh command: `npm run data:china`.
+
+The source snapshot is useful for structured profile selection. It is not a substitute for an address-level geocoder: coordinate precision is administrative-area-centre precision.

frontend/src/data/china-locations.ts

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+import source from "./china-locations.json";
+
+export type LocationNode = {
+  code: string;
+  name: string;
+  center: [longitude: number, latitude: number];
+};
+
+export type CityNode = LocationNode & {
+  districts: LocationNode[];
+};
+
+export type ProvinceNode = LocationNode & {
+  cities: CityNode[];
+};
+
+export type ChinaLocationData = {
+  source: {
+    name: string;
+    url: string;
+    license: string;
+    generatedAt: string;
+  };
+  country: {
+    code: "CN";
+    name: string;
+    timezone: number;
+    provinces: ProvinceNode[];
+  };
+};
+
+export const chinaLocations = source as ChinaLocationData;