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/date_view.rs

@@ -121,13 +121,39 @@ pub fn day_start_instant(day: NaiveDate, zone: Tz) -> i64 {
 /// exact call in Rust without a row being dropped first.
 pub const LEGACY_INSTANT_BAND_SECS: i64 = 15 * 3600;
 
+/// Fold calendar-day filter params (`date_from_day` / `date_to_day`,
+/// `YYYY-MM-DD`) into the instant bounds: the first day's start and the
+/// last day's end in the owner's display zone, the same days `/memories`
+/// groups by (#152). A day param replaces its instant counterpart; an
+/// unparseable one is ignored. `zone` is only called when a day is given,
+/// so requests without them never read prefs.
+pub fn apply_day_bounds(
+    from: &mut Option<i64>,
+    to: &mut Option<i64>,
+    from_day: Option<&str>,
+    to_day: Option<&str>,
+    zone: impl FnOnce() -> Tz,
+) {
+    if from_day.is_none() && to_day.is_none() {
+        return;
+    }
+    let zone = zone();
+    let parse = |d: &str| NaiveDate::parse_from_str(d.trim(), "%Y-%m-%d").ok();
+    if let Some(day) = from_day.and_then(parse) {
+        *from = Some(day_start_instant(day, zone));
+    }
+    if let Some(next) = to_day.and_then(parse).and_then(|d| d.succ_opt()) {
+        *to = Some(day_start_instant(next, zone) - 1);
+    }
+}
+
 /// An inclusive true-instant range (`date_from` / `date_to` on the photo
 /// listing endpoints), plus the zones [`row_true_instant`] needs to read
 /// unconverted rows. Either bound may be open.
 ///
 /// Bounds are instants, never wall clocks: a client filtering by calendar
-/// day sends that day's midnights in the owner's display zone (see
-/// `nl_query::iso_to_unix`), so the range agrees with
+/// day sends `date_from_day` / `date_to_day` and the handler turns them into
+/// display-zone day bounds ([`apply_day_bounds`]), so the range agrees with
 /// [`row_display_day`] grouping by construction.
 #[derive(Clone, Copy, Debug)]
 pub struct InstantRange {
@@ -698,6 +724,52 @@ mod tests {
         );
     }
 
+    #[test]
+    fn day_bounds_are_the_display_zone_day() {
+        // July 5 is a different stretch of instants for a NY and a Tokyo
+        // owner; the device's zone plays no part (#152).
+        let (mut from, mut to) = (None, None);
+        apply_day_bounds(
+            &mut from,
+            &mut to,
+            Some("2024-07-05"),
+            Some("2024-07-05"),
+            ny,
+        );
+        assert_eq!((from, to), (Some(1_720_152_000), Some(1_720_238_399)));
+        let (mut from, mut to) = (None, None);
+        apply_day_bounds(
+            &mut from,
+            &mut to,
+            Some("2024-07-05"),
+            Some("2024-07-05"),
+            || Tz::Asia__Tokyo,
+        );
+        assert_eq!((from, to), (Some(1_720_105_200), Some(1_720_191_599)));
+        // A 23-hour DST day still ends at the next midnight.
+        let (mut from, mut to) = (None, None);
+        apply_day_bounds(
+            &mut from,
+            &mut to,
+            Some("2024-03-10"),
+            Some("2024-03-10"),
+            ny,
+        );
+        assert_eq!((from, to), (Some(1_710_046_800), Some(1_710_129_599)));
+    }
+
+    #[test]
+    fn day_bounds_replace_their_side_only_and_skip_bad_input() {
+        let (mut from, mut to) = (Some(1), Some(2));
+        apply_day_bounds(&mut from, &mut to, None, Some("2024-07-05"), ny);
+        assert_eq!((from, to), (Some(1), Some(1_720_238_399)));
+        let (mut from, mut to) = (Some(1), Some(2));
+        apply_day_bounds(&mut from, &mut to, Some("July 5th"), None, ny);
+        assert_eq!((from, to), (Some(1), Some(2)));
+        // No day params: the zone (a prefs read) is never asked for.
+        apply_day_bounds(&mut from, &mut to, None, None, || panic!("zone read"));
+    }
+
     #[test]
     fn display_day_respects_a_non_new_york_display_zone() {
         // Owner in Tokyo: 2024-07-05 01:30 UTC = 10:30 JST July 5 (not