Explore Gazet-powered natural-language AOI search

## Summary

Explore using [Gazet](https://github.com/developmentseed/gazet) — Development Seed's natural-language geocoding tool with GIS operations over Overture/Natural Earth data — to let users type a query like "50km buffer around Paris" and get back a GeoJSON AOI polygon, feeding directly into the AOI pipeline shipped in #90.

## Why

#90 added AOI loading via GeoJSON file upload. Gazet could offer a second, more casual way to define an AOI — typed natural language instead of a prepared file — for cases where the user doesn't already have a GeoJSON (e.g. "I just want a buffer around a city," not a precise rapid-mapping polygon).

## Proposed approach

- Gazet exposes a FastAPI `/search` endpoint that returns GeoJSON (`FeatureCollection`/`Feature`) for a natural-language query.
- Feed the returned GeoJSON through the existing AOI pipeline rather than building a parallel code path: `loadAoiFromFile`-style normalization → `filterStore.setAoi()` → `map.fitBounds()` (same as `AoiUpload.tsx` / `aoiUtils.ts`).
- Positioned as complementary to file upload, not a replacement — a second entry point into the same AOI state.

## Dependency risk (needs resolving before scoping further)

- Development Seed has a hosted Gazet instance, but it currently appears to be down/unreliable. Need to confirm status, ownership, and uptime expectations before committing to a UI build — no point building a search box against a service that isn't reliably available.
- If the hosted instance isn't viable, this may require deploying/maintaining our own instance (Gazet ships a Dockerfile/docker-compose), which is a bigger lift than the search UI itself.

## Open questions

- Does Gazet support buffer distances natively in the query (e.g. "50km buffer around Paris"), or would we need to parse a distance + place and construct the buffer ourselves (e.g. with Turf, matching the geometry libraries already used in `aoiUtils.ts`)?
- What's the reliability/ownership story for the hosted instance?
- Should this be gated behind a feature flag until Gazet's hosting story is settled?

First verify the hosted Gazet /search service's status, ownership, and uptime expectations before scoping implementation. Then read AoiUpload.tsx, aoiUtils.ts, and the AOI pipeline from #90 to understand the existing normalization, filterStore.setAoi(), and map.fitBounds() flow. Done means choosing a viable hosting or feature-flag approach and defining whether Gazet or local geometry handling supports the proposed queries.

Written by the indexing model from the issue text.