Add Flights Map C.1 implementation plan and updated spec

Spec: narrows useCityName handling (leave untouched due to active
consumers). Plan: 10 TDD tasks covering types, api, transform rules,
helpers, hook, barrel, page wiring, and regression tests.

docs/superpowers/specs/2026-04-17-flights-map-c1-dictionaries-design.md

@@ -31,7 +31,7 @@ src/shared/dictionaries/
 └── <co-located .test.ts / .test.tsx files>
 ```
 
-`useCityName` in `src/shared/hooks/useDictionaries.ts` is removed — it was a passthrough stub that nobody else should depend on; a targeted grep during implementation confirms this before deletion.
+`useCityName` in `src/shared/hooks/useDictionaries.ts` stays as-is. It has active consumers (`StationDisplay`, `PopularRequestItem`) that expect synchronous code→string passthrough, which the new dictionaries hook does not provide. Migration of those callers to the real dictionaries is out of scope for C.1 and will be handled later if/when it becomes worthwhile.
 
 ## Types
 
@@ -225,4 +225,4 @@ Using `@testing-library/react`'s `renderHook`:
 
 - **Endpoint shape.** We're assuming `/dictionary/1/{world_regions|countries|cities|airports}` with no locale segment (Angular parity). If prod returns a different path at integration time, we adjust `api.ts`. This is a known-unknown, not a blocker.
 - **Australia filter.** Carried over as a direct parity port (`world_region_id === 500373`). If product wants to revisit this, it's a one-line change.
-- **`useCityName` stub removal.** `grep` the repo during implementation; if anything still consumes it, update the caller to pull from `useDictionaries().dictionaries?.cityByCode.get(code)?.name` instead.
+- **`useCityName` stub.** Left untouched in C.1 because of active consumers; see Architecture note above.