feat(dates): photo date filters on the true instant (#152)

date_from / date_to on /photos, /photos/exif and unified search ran on
the legacy mixed-convention date_taken, so a photo could display inside
a range yet be filtered out of it by up to its UTC offset (or by years,
for rows the filename class re-dated).

The filter lives in the shared ExifDao::query_by_exif, so it's fixed
once there:

- query_by_exif takes Option<date_view::InstantRange> (bounds + display
  and server zones) instead of raw date_from / date_to.
- SQL pre-filter: converted rows on date_utc exactly; unconverted rows
  (drain pending, permanent floor) on date_taken widened by
  LEGACY_INSTANT_BAND_SECS (±15 h, now shared with /memories). Converted
  rows are deliberately not bounded by date_taken: a re-dated row's
  legacy value can sit years from its instant.
- Exact pass in Rust via InstantRange::contains → row_true_instant, so
  every returned row's true instant is inside the range.

Calendar days now mean the owner's days: nl_query::iso_to_unix builds
day bounds in the display zone (it used UTC midnights, which only lined
up with the legacy wall-as-UTC column), and unified search's "today" is
the owner's today rather than UTC's. The midnight-with-DST-gap fallback
moves from memories_anchor into date_view::day_start_instant.

Compatibility: clients already sending real instants (Apollo's
/photos/exif windows) get correct edges with no change. Clients sending
UTC-midnight day bounds see ranges shift by up to the UTC offset until
they send display-zone bounds.

No index on date_utc; the OR clause scans, which is milliseconds at
personal-library scale (same as /memories today).

dev/e2e check gains /photos/exif wall_clock + true_instant assertions and
range-edge checks ([t, t] in, [.., t-1] and [t+1, ..] out). Not run here:
the harness needs the WSL + Windows toolchain.

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

CLAUDE.md

@@ -520,6 +520,10 @@ GET /image/metadata?path=...
 
 // Advanced search with filters
 GET /photos?path=...&recursive=true&sort=DateTakenDesc&camera_make=Canon&gps_lat=...&gps_lon=...&gps_radius_km=10&date_from=...&date_to=...&tag_ids=1,2,3&media_type=Photo
+//   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.
 
 // Video streaming (HLS)
 POST /video/generate (creates .m3u8 playlist + .ts segments)