Derived clips: link MP4 versions, list them apart, video Enhance output

Groundwork for Enhance "Animate" (#208): a video made from a photo.

- Version linking reads the XMP link from MP4 / MOV too (top-level uuid box
  with the XMP UUID, mdat seeked over), at ingest and on Enhance approve.
- New kind `animated`, a derived clip (CLIP_KINDS): hidden behind the photo
  like a version, but not counted in photo_version_counts / version_count,
  never a display choice (400 clip_not_displayable), and listed as `clips`
  in GET /image/versions. Approve returns the clip entry.
- Templates whose imageapi:save is ImageApiSaveVideoVersion report
  output "video" in /enhance/templates (no enhance.toml change). Previews
  already relay ComfyUI's content type (video/mp4).

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

src/enhance/handlers.rs

@@ -221,6 +221,8 @@ struct TemplateView {
     /// Approximate output size; clients warn when the original is larger.
     output_megapixels: f64,
     warn_above_megapixels: f64,
+    /// `image` (a PNG version) or `video` (an MP4 clip, e.g. Animate).
+    output: super::template::OutputKind,
 }
 
 #[get("/enhance/templates")]
@@ -248,6 +250,7 @@ pub async fn get_templates(_: Claims, svc: web::Data<EnhanceService>) -> impl Re
             default: default.as_deref() == Some(t.cfg.name.as_str()),
             output_megapixels: t.cfg.output_megapixels,
             warn_above_megapixels: svc.config.warn_above_megapixels,
+            output: t.output,
         })
         .collect();
     let mut body = json!({
@@ -538,7 +541,13 @@ pub async fn approve(
         };
         build_response(dao.as_mut(), &original, job.library_id)
             .ok()
-            .and_then(|r| r.versions.into_iter().find(|v| v.hash == hash))
+            // An approved clip (Animate) is listed under `clips`.
+            .and_then(|r| {
+                r.versions
+                    .into_iter()
+                    .chain(r.clips)
+                    .find(|v| v.hash == hash)
+            })
     };
     match entry {
         Some(v) => HttpResponse::Ok().json(v),