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/data/mod.rs

@@ -259,6 +259,10 @@ pub struct MetadataResponse {
     pub filename_date: Option<i64>, // Date extracted from filename
     pub library_id: Option<i32>,
     pub library_name: Option<String>,
+    /// The capture wall clock to display, naive ISO-8601
+    /// (`2018-09-29T14:00:00`) — `date_view::file_wall_clock`. Render it
+    /// verbatim; never zone-convert it (ADR-0001).
+    pub wall_clock: Option<String>,
 }
 
 impl From<fs::Metadata> for MetadataResponse {
@@ -277,6 +281,7 @@ impl From<fs::Metadata> for MetadataResponse {
             filename_date: None, // Will be set in endpoint handler
             library_id: None,
             library_name: None,
+            wall_clock: None, // Set in the endpoint handler
         }
     }
 }
@@ -437,6 +442,9 @@ pub struct GpsPhotoSummary {
     /// Which evidence pinned the instant (`offset_tag`, `gps`,
     /// `assumed_server`, `utc_direct`, `manual`).
     pub date_taken_tz_source: Option<String>,
+    /// Capture wall clock to display (naive ISO-8601; see
+    /// `MetadataResponse::wall_clock`).
+    pub wall_clock: Option<String>,
 }
 
 #[derive(Debug, Serialize)]