dev/e2e: wall_clock regression check + deterministic fixture dates

`e2e.sh check` compares every indexed fixture's manifest wall clock with
the `wall_clock` reported by /image/metadata, /memories and
/photos/gps-summary; any disagreement fails.

- Fixture videos are stamped like phone containers: the America/New_York
  wall as a UTC creation_time (the label previously showed the UTC time).
- mtimes are pinned in America/New_York instead of the host's zone.
- The e2e env sets TZ=America/New_York (the #120 preflight): the Windows
  exe has no /etc/timezone, so server_zone() was otherwise None.

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

dev/e2e/README.md

@@ -7,6 +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
 ```
 
 Log in from the app with **server** `http://10.0.2.2:8090` (Android
@@ -32,8 +33,11 @@ server. Everything under `.work/` is gitignored and safe to delete.
 `gen_fixtures.py` renders every image with its relative path, date and
 scenario burned into the pixels — a screenshot tells you exactly which
 fixture is on screen. `.work/state/manifest.json` lists every item with its
-expected date, GPS, camera, tags and duplicate relationship, plus expected
-counts; assert against it rather than hardcoding.
+expected date, GPS, camera, tags, duplicate relationship and **expected
+`wall_clock`** (the capture time the UI must show), plus expected counts;
+assert against it rather than hardcoding. Naive fixture times are walls in
+America/New_York (the e2e display and server zone); videos are stamped the
+way phones write containers (that wall, as a UTC `creation_time`).
 
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