docs: date_from_day / date_to_day on the photo listing endpoints

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -523,7 +523,10 @@ GET /photos?path=...&recursive=true&sort=DateTakenDesc&camera_make=Canon&gps_lat
 //   date_from / date_to are inclusive TRUE INSTANTS, matched against each row's
 //   true instant (date_utc, else date_view::row_true_instant's fallback) in
 //   ExifDao::query_by_exif — shared by /photos, /photos/exif and unified search.
-//   A calendar-day range = that day's bounds in the owner's display zone.
+//   For calendar days send date_from_day / date_to_day (YYYY-MM-DD) instead: the
+//   handler turns them into the days' bounds in the owner's display zone
+//   (date_view::apply_day_bounds), each replacing its instant counterpart, so
+//   clients never compute midnights in the device's zone.
 
 // Natural-language search (LLM translates q into filters + a CLIP term)
 GET /photos/search/unified?q=...&model=...&interpret=true