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/template.rs

@@ -19,6 +19,19 @@ pub const TITLE_REFERENCE: &str = "imageapi:reference";
 /// Prompt-node inputs, in the order they are tried.
 const PROMPT_INPUTS: &[&str] = &["text", "prompt", "value"];
 
+/// What a template produces, from its `imageapi:save` node's class.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize)]
+#[serde(rename_all = "lowercase")]
+pub enum OutputKind {
+    /// Save Image Version: PNG versions.
+    Image,
+    /// Save Video Version: an MP4 (e.g. a clip animated from the photo).
+    Video,
+}
+
+/// The save node class that makes a template's output a video.
+pub const VIDEO_SAVE_CLASS: &str = "ImageApiSaveVideoVersion";
+
 /// Output nodes that write into ComfyUI's output folder on every API run.
 const STRAY_OUTPUT_CLASSES: &[&str] = &[
     "SaveImage",
@@ -38,6 +51,8 @@ pub struct Template {
     /// `(node id, input name)` of the prompt text.
     prompt: Option<(String, &'static str)>,
     reference_id: Option<String>,
+    /// Image or video, from the save node's class.
+    pub output: OutputKind,
     /// Startup warnings (stray output nodes).
     pub warnings: Vec<String>,
 }
@@ -143,6 +158,11 @@ impl Template {
                 ));
             }
         }
+        let output = if workflow[&save_id]["class_type"].as_str() == Some(VIDEO_SAVE_CLASS) {
+            OutputKind::Video
+        } else {
+            OutputKind::Image
+        };
         Ok(Template {
             cfg,
             workflow,
@@ -150,6 +170,7 @@ impl Template {
             save_id,
             prompt,
             reference_id,
+            output,
             warnings,
         })
     }
@@ -414,6 +435,23 @@ mod tests {
         assert_ne!(input(&x.prompt, "5", "seed"), input(&y.prompt, "5", "seed"));
     }
 
+    #[test]
+    fn output_kind_follows_the_save_node() {
+        assert_eq!(
+            load(RESTORE, PromptMode::Append).unwrap().output,
+            OutputKind::Image
+        );
+        let video = RESTORE.replace(
+            "\"ImageApiSaveImageVersion\"",
+            "\"ImageApiSaveVideoVersion\"",
+        );
+        assert_ne!(video, RESTORE);
+        assert_eq!(
+            load(&video, PromptMode::Append).unwrap().output,
+            OutputKind::Video
+        );
+    }
+
     #[test]
     fn random_seeds_fit_seedvr2s_u32_limit() {
         // SeedVR2VideoUpscaler rejects seeds above 2^32 - 1 at validation.