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>

dev/e2e/README.md

@@ -7,7 +7,7 @@ end-to-end and agent-driven UI testing of the SynologyFileViewer app.
 dev/e2e/e2e.sh up        # build + fixtures + reset + start; blocks until ingest is done
 dev/e2e/e2e.sh reset     # back to the pristine baseline (after tests mutate things)
 dev/e2e/e2e.sh stop
-dev/e2e/e2e.sh check     # every fixture's displayed capture time (wall_clock) vs the manifest
+dev/e2e/e2e.sh check     # every fixture's wall_clock + true_instant vs the manifest, and /photos/exif range edges
 ```
 
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