Add data model types, datetime utils, and dictionary hook

Port Angular flight types (ISimpleFlight, IFlightLeg, ITimesSet, etc.)
to minimal React-friendly interfaces. Add formatDuration/formatTime/
formatDate/isDayChange as pure functions. Stub useCityName hook as
passthrough pending customer dictionary API endpoint.

src/shared/hooks/useDictionaries.test.ts

@@ -0,0 +1,18 @@
+import { describe, it, expect } from "vitest";
+import { useCityName } from "./useDictionaries.js";
+
+describe("useCityName", () => {
+  it("returns the code itself (Phase 2 passthrough)", () => {
+    expect(useCityName("SVO")).toBe("SVO");
+  });
+
+  it("returns the code for any input", () => {
+    expect(useCityName("LED")).toBe("LED");
+    expect(useCityName("MOW")).toBe("MOW");
+    expect(useCityName("JFK")).toBe("JFK");
+  });
+
+  it("handles empty string", () => {
+    expect(useCityName("")).toBe("");
+  });
+});

src/shared/hooks/useDictionaries.ts

@@ -0,0 +1,22 @@
+/**
+ * Airport/city dictionary hooks.
+ *
+ * Phase 2 stub: returns the IATA code itself as the city name.
+ * The real implementation will call the customer's dictionary API
+ * (similar to Angular DictionariesService.getCityOrAirport).
+ *
+ * TODO: Replace passthrough with actual API call once the dictionary
+ * endpoint is provided by the customer. The Angular app loads dictionaries
+ * via networkService.getDictionary('cities') / getDictionary('airports')
+ * and builds an in-memory Map<code, CityModel>.
+ */
+
+/**
+ * Returns the city name for a given IATA airport/city code.
+ *
+ * Phase 2: passthrough — returns the code itself.
+ */
+export function useCityName(code: string): string {
+  // TODO: Look up from dictionary cache/API when available
+  return code;
+}