feat: places (reverse geocoding) + folder browser

Places:
- worker/geocode.js: Nominatim reverse geocoder, 1 req/sec rate limit,
  in-memory cache keyed to 3-decimal-place coordinates
- Ingest calls reverseGeocode() for any photo with GPS data; stores
  place_city and place_country on the photo row
- DB migrations add place_city / place_country columns + index on place_city
- Stats API returns cities grouped by count
- buildFilter() supports ?city= parameter
- FilterSidebar shows a Places section with city list + country sublabel

Folder browser:
- GET /api/fs/browse?path=… lists subdirectories (path-normalized to prevent traversal)
- Settings panel: 📁 button opens inline directory browser below the add
  input — navigate with up arrow / directory clicks, Select fills the input

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/api/photos.js

@@ -10,7 +10,7 @@ const json = (body) => ({
 });
 
 // Library
-export function fetchPhotos({ cursor, limit = 100, q, from, to, tagId, collectionId, starred } = {}) {
+export function fetchPhotos({ cursor, limit = 100, q, from, to, tagId, collectionId, starred, city } = {}) {
   const p = new URLSearchParams({ limit });
   if (cursor)       p.set('cursor',       cursor);
   if (q)            p.set('q',            q);
@@ -19,9 +19,14 @@ export function fetchPhotos({ cursor, limit = 100, q, from, to, tagId, collectio
   if (tagId)        p.set('tagId',        tagId);
   if (collectionId) p.set('collectionId', collectionId);
   if (starred)      p.set('starred',      starred);
+  if (city)         p.set('city',         city);
   return api(`/api/photos?${p}`);
 }
 
+export function fetchDirBrowser(dirPath) {
+  return api(`/api/fs/browse?path=${encodeURIComponent(dirPath)}`);
+}
+
 export function fetchPhotoDetail(id) {
   return api(`/api/photos/${id}`);
 }