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/handlers/image.rs

@@ -524,11 +524,18 @@ pub async fn get_file_metadata(
                 .map(memories::FilenameDate::legacy_timestamp);
 
             // Query EXIF data if available
-            if let Ok(mut dao) = exif_dao.lock()
-                && let Ok(Some(exif)) = dao.get_exif(&path.path)
-            {
-                response.exif = Some(exif.into());
-            }
+            let row = exif_dao
+                .lock()
+                .ok()
+                .and_then(|mut dao| dao.get_exif(&path.path).ok().flatten());
+            response.wall_clock = crate::date_view::file_wall_clock(
+                row.as_ref(),
+                &path.path,
+                earliest_fs_time(&response),
+                crate::date_view::owner_display_zone(&app_state.user_ai_prefs_dao),
+                crate::camera_tz::server_zone(),
+            );
+            response.exif = row.map(Into::into);
 
             span.add_event(
                 "Metadata fetched",
@@ -706,8 +713,16 @@ pub async fn set_image_gps(
                     filename_date: None,
                     library_id: None,
                     library_name: None,
+                    wall_clock: None,
                 },
             };
+            response.wall_clock = crate::date_view::file_wall_clock(
+                Some(&row),
+                &normalized_path,
+                earliest_fs_time(&response),
+                crate::date_view::owner_display_zone(&app_state.user_ai_prefs_dao),
+                crate::camera_tz::server_zone(),
+            );
             response.exif = Some(row.into());
             response.library_id = Some(resolved_library.id);
             response.library_name = Some(resolved_library.name.clone());
@@ -848,6 +863,7 @@ fn build_metadata_response_for_date_mutation(
     library: &libraries::Library,
     rel_path: &str,
     exif: ImageExif,
+    display_zone: chrono_tz::Tz,
 ) -> MetadataResponse {
     let full_path = is_valid_full_path(&library.root_path, &rel_path.to_string(), false);
     let fs_meta = full_path
@@ -864,8 +880,16 @@ fn build_metadata_response_for_date_mutation(
             filename_date: None,
             library_id: None,
             library_name: None,
+            wall_clock: None,
         },
     };
+    response.wall_clock = crate::date_view::file_wall_clock(
+        Some(&exif),
+        rel_path,
+        earliest_fs_time(&response),
+        display_zone,
+        crate::camera_tz::server_zone(),
+    );
     response.exif = Some(exif.into());
     response.library_id = Some(library.id);
     response.library_name = Some(library.name.clone());
@@ -874,6 +898,15 @@ fn build_metadata_response_for_date_mutation(
     response
 }
 
+/// Earlier of the file's created / modified times — the ingest waterfall's
+/// `fs_time` rule — for the wall-clock fallback of unindexed files.
+fn earliest_fs_time(response: &MetadataResponse) -> Option<i64> {
+    match (response.created, response.modified) {
+        (Some(c), Some(m)) => Some(c.min(m)),
+        (c, m) => c.or(m),
+    }
+}
+
 #[post("/image/exif/date")]
 #[tracing::instrument(name = "set_image_date", skip_all)]
 pub async fn set_image_date(
@@ -924,6 +957,7 @@ pub async fn set_image_date(
                 library,
                 &normalized_path,
                 row,
+                crate::date_view::owner_display_zone(&app_state.user_ai_prefs_dao),
             ))
         }
         Err(e) => {
@@ -972,6 +1006,7 @@ pub async fn clear_image_date(
                 library,
                 &normalized_path,
                 row,
+                crate::date_view::owner_display_zone(&app_state.user_ai_prefs_dao),
             ))
         }
         Err(e) => {