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/versions/handlers.rs

@@ -12,7 +12,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::data::Claims;
 use crate::database::ExifDao;
-use crate::database::version_dao::VersionDao;
+use crate::database::version_dao::{VersionDao, is_clip_kind};
 use crate::libraries;
 use crate::state::AppState;
 use crate::utils::normalize_path;
@@ -66,6 +66,9 @@ pub struct VersionsResponse {
     /// standalone photos).
     pub original: Option<FileRef>,
     pub versions: Vec<VersionEntry>,
+    /// Derived clips: videos made from the photo (kind `animated`). Same
+    /// shape as `versions`, but never a display choice.
+    pub clips: Vec<VersionEntry>,
     /// The globally displayed version; `null` = the original.
     pub display_hash: Option<String>,
 }
@@ -137,6 +140,7 @@ pub fn build_response(
 
     let files = dao.list_versions(original_hash)?;
     let mut versions = Vec::with_capacity(files.len());
+    let mut clips = Vec::new();
     for f in files {
         let reference_hashes = dao.list_references(&f.version_hash)?;
         let located = dao.files_for_hashes(&reference_hashes, Some(f.library_id))?;
@@ -151,7 +155,12 @@ pub fn build_response(
                 }
             })
             .collect();
-        versions.push(VersionEntry {
+        let list = if is_clip_kind(&f.kind) {
+            &mut clips
+        } else {
+            &mut versions
+        };
+        list.push(VersionEntry {
             path: f.rel_path,
             library_id: f.library_id,
             hash: f.version_hash,
@@ -177,6 +186,7 @@ pub fn build_response(
     Ok(VersionsResponse {
         original,
         versions,
+        clips,
         display_hash,
     })
 }
@@ -241,6 +251,13 @@ pub async fn put_display(
                     return ApiError::internal("internal error").into_response();
                 }
             };
+        if current.clips.iter().any(|c| c.hash == hash) {
+            return ApiError::bad_request(
+                "clip_not_displayable",
+                "A clip made from this photo can't be shown in its place",
+            )
+            .into_response();
+        }
         if !current.versions.iter().any(|v| v.hash == hash) {
             return ApiError::bad_request(
                 "not_a_version",