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/check_wall_clock.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""Regression check for the displayed capture time (ADR-0001 `wall_clock`).
+
+For every indexed fixture, the manifest's expected wall clock must equal the
+`wall_clock` the server reports on each endpoint that includes the file:
+`/image/metadata`, `/memories` (today's day span) and `/photos/gps-summary`.
+One disagreement anywhere is exactly the class of bug this field exists to
+end, so any mismatch fails the run.
+
+Usage: check_wall_clock.py <manifest.json>   (run via `e2e.sh check`)
+"""
+
+import json
+import os
+import subprocess
+import sys
+import urllib.parse
+from pathlib import Path
+
+E2E = Path(__file__).with_name("e2e.sh")
+
+
+def api(path: str) -> dict:
+    return json.loads(subprocess.check_output([str(E2E), "api", "GET", path]))
+
+
+def main() -> int:
+    manifest = json.load(open(sys.argv[1]))
+    excluded = tuple(d.strip("/") + "/" for d in manifest["excluded_dirs"])
+    items = [i for i in manifest["items"] if not i["path"].startswith(excluded)]
+
+    memories = {m["path"]: m.get("wall_clock") for m in api("memories?span=day")["items"]}
+    gps = {g["path"]: g.get("wall_clock") for g in api("photos/gps-summary?path=")["photos"]}
+
+    failures = 0
+    for item in items:
+        path, want = item["path"], item["wall_clock"]
+        got = {"metadata": api("image/metadata?path=" + urllib.parse.quote(path)).get("wall_clock")}
+        if path in memories:
+            got["memories"] = memories[path]
+        if path in gps:
+            got["gps-summary"] = gps[path]
+        bad = {k: v for k, v in got.items() if v != want}
+        if bad:
+            failures += 1
+            print(f"MISMATCH {path}: expected {want}, got {bad}")
+
+    print(f"{len(items) - failures}/{len(items)} fixtures report the expected wall clock "
+          f"({len(memories)} in memories, {len(gps)} in gps-summary)")
+    return 1 if failures else 0
+
+
+if __name__ == "__main__":
+    os.environ.setdefault("E2E_TOKEN", subprocess.check_output([str(E2E), "token"], text=True).strip())
+    sys.exit(main())