Dates: serve the display wall clock (wall_clock) to clients

Every payload a client renders a capture time from now carries
`wall_clock`, a naive ISO-8601 string computed by the existing
`date_view::row_display_wall`: the camera's wall clock (true instant +
camera offset; the owner's display zone without an offset), with the
per-source fallback for unconverted rows. Clients render it verbatim and
do no zone math, which is the FileViewer-React #33 / Apollo #37 flip with
the rule kept server-side: the drain's permanent `date_utc IS NULL` floor
(#120: edited/exported files) would otherwise force every client to
carry the per-source legacy conventions forever, and insight prompts
already use the same function, so prompt and UI agree by construction.

- `/image/metadata` (+ the GPS / date / date-clear mutation responses):
  `file_wall_clock` — the row's wall, else the filename-class date, else
  the earliest fs time in the display zone (unindexed files).
- `/memories` items and `/photos/gps-summary` photos: `row_wall_clock`.
- `get_all_with_gps` returns full rows instead of a 7-tuple that dropped
  `date_taken_source`, which unconverted rows need.
- `date_view::owner_display_zone` resolves prefs -> app default per request.

Legacy fields are untouched, so current clients see byte-identical
responses (additive; safe to deploy ahead of the client flip, per #120).

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

src/reels/selector.rs

@@ -430,6 +430,7 @@ mod tests {
                 date_utc: None,
                 camera_offset_minutes: None,
                 date_taken_tz_source: None,
+                wall_clock: None,
             },
             memories::MemoryItem {
                 path: "b".into(),
@@ -439,6 +440,7 @@ mod tests {
                 date_utc: None,
                 camera_offset_minutes: None,
                 date_taken_tz_source: None,
+                wall_clock: None,
             },
             memories::MemoryItem {
                 path: "c".into(),
@@ -448,6 +450,7 @@ mod tests {
                 date_utc: None,
                 camera_offset_minutes: None,
                 date_taken_tz_source: None,
+                wall_clock: None,
             },
         ];
         assert_eq!(
@@ -466,6 +469,7 @@ mod tests {
             date_utc: None,
             camera_offset_minutes: None,
             date_taken_tz_source: None,
+            wall_clock: None,
         }
     }
     fn item_at(ts: i64, name: &str) -> memories::MemoryItem {