feat(dates): calendar-day date filters in the owner's display zone (#152)

/photos, /photos/exif and unified search take date_from_day /
date_to_day (YYYY-MM-DD): the server turns them into the first day's
start and the last day's end in the owner's display zone, the same days
/memories groups by. Each replaces its instant counterpart. Clients stop
computing midnights in the device's zone, which drifted by the travel
offset whenever the phone's zone differed from display_tz.

e2e check: every fixture is included by its display-zone day and
excluded by the days either side.

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

src/data/mod.rs

@@ -153,9 +153,13 @@ pub struct FilesRequest {
 
     // Date range filtering: inclusive true instants (unix seconds), compared
     // against each row's true instant (ADR-0001, #152). For calendar days,
-    // send the day's bounds in the owner's display zone.
+    // send `date_from_day` / `date_to_day` (`YYYY-MM-DD`) instead: the server
+    // takes their bounds in the owner's display zone, and each replaces its
+    // instant counterpart.
     pub date_from: Option<i64>,
     pub date_to: Option<i64>,
+    pub date_from_day: Option<String>,
+    pub date_to_day: Option<String>,
 
     // Media type filtering
     pub media_type: Option<MediaType>,
@@ -538,6 +542,10 @@ pub struct ExifBatchRequest {
     pub date_from: Option<i64>,
     /// Upper bound (inclusive). Same semantics as `date_to` on `/photos`.
     pub date_to: Option<i64>,
+    /// Calendar-day bounds (`YYYY-MM-DD`) in the owner's display zone; each
+    /// replaces its instant counterpart. Same as on `/photos`.
+    pub date_from_day: Option<String>,
+    pub date_to_day: Option<String>,
     /// Restrict results to a single library by id. Omit (or "" / "all") for
     /// union mode — the default. Filtered post-query in the handler so the
     /// existing `query_by_exif` DAO trait stays untouched.