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>

CLAUDE.md

@@ -360,7 +360,12 @@ hash — design it alongside Branch D.
 
 A **version** is a non-destructive restoration, upscale or edit of a photo that
 an external process (the ComfyUI node in `comfyui-imageapi-versions`) writes next
-to the original, as `<dir>/aiedits/<original name>.<kind>[.<n>].png`. ImageApi
+to the original, as `<dir>/aiedits/<original name>.<kind>[.<n>].png`. A
+**derived clip** (kind `animated`, `CLIP_KINDS`) is a video made from a photo
+(Enhance "Animate", `<name>.animated[.<n>].mp4`): linked, hidden and lifecycled
+exactly like a version, but never counted as one (`photo_version_counts`,
+`version_count`), never a display choice (`PUT /image/versions/display` answers 400
+`clip_not_displayable`), and listed apart, as `clips` in `GET /image/versions`. ImageApi
 only detects it (library roots stay read-only) and shows original + versions as
 **one photo**; a *global* choice (not per user) says which file is displayed.
 Code: `src/database/version_dao.rs` (tables, DAO, SQL predicates),
@@ -376,8 +381,9 @@ for the `link_versions` binary).
   global choice; no row = the original, and a display file with no live row reads as
   the original.
 - **Linking at ingest** (`watcher::process_new_files`, before any derived work):
-  (1) a PNG's XMP `xmpMM:DerivedFrom/stRef:documentID = blake3:<hex>` (iTXt chunk
-  `XML:com.adobe.xmp`, read by hand, no decode); (2) the file-name convention next
+  (1) the file's XMP `xmpMM:DerivedFrom/stRef:documentID = blake3:<hex>`: a PNG's
+  iTXt chunk `XML:com.adobe.xmp`, or an MP4 / MOV's top-level `uuid` box with the XMP
+  UUID (both read by hand, no decode; `mdat` is seeked over); (2) the file-name convention next
   to an indexed original in the same library (same dir, or the parent of
   `aiedits/`). Name links are retried every tick (`sweep_name_links`, paged by a
   per-library resume cursor that wraps, so candidates that never resolve can't starve
@@ -455,7 +461,9 @@ auth and stays LAN-only, so ImageApi relays previews too.
   `file`, `prompt_mode`, `prompt_join`, `output_megapixels`).
 - **Templates** are API-format workflow exports, read-only (never edit them from
   here). Nodes are found by `_meta.title`: `imageapi:source` (required, gets the
-  photo path), `imageapi:save` (required, forced to `require_approval = true`),
+  photo path), `imageapi:save` (required, forced to `require_approval = true`; a
+  `ImageApiSaveVideoVersion` there makes the template's `output` `video`, an MP4 clip,
+  else `image`),
   `imageapi:prompt` (optional; fills the first of `text` / `prompt` / `value`),
   `imageapi:reference` (optional). `prompt_mode = "append"`: the user's text is joined
   after the template's own prompt with `prompt_join` (default one space); empty text
@@ -503,7 +511,7 @@ GET  /enhance/templates
       "templates": [{"name","label","description","accepts_prompt",
                      "prompt_mode": "append"|"replace", "prompt_required",
                      "accepts_reference","default","output_megapixels",
-                     "warn_above_megapixels"}]}
+                     "warn_above_megapixels", "output": "image"|"video"}]}
 POST /enhance  {"path","template","prompt"?,"reference_path"?,"library"?}  -> job
 GET  /enhance/jobs/{id}              -> job
 GET  /enhance/jobs?path=&library=    -> {"jobs": [job, ...]}  newest first, discarded hidden
@@ -511,8 +519,9 @@ GET  /enhance/prompts?templates=a,b&limit=10  (templates optional = all; limit 1
   -> {"prompts": [{"prompt","template","last_used","uses"}]}  distinct trimmed prompts, newest
      use first; template/last_used from the newest job; discarded + failed jobs count;
      DB only (no library scope, answers even when ComfyUI is down or Enhance is off)
-GET  /enhance/jobs/{id}/preview/{n}  -> the staged PNG (relayed from ComfyUI /view)
-POST /enhance/jobs/{id}/approve {"n"} -> a /image/versions `versions[]` entry
+GET  /enhance/jobs/{id}/preview/{n}  -> the staged PNG or MP4 (relayed from ComfyUI /view,
+                                        with its content type)
+POST /enhance/jobs/{id}/approve {"n"} -> a /image/versions `versions[]` (or `clips[]`) entry
 POST /enhance/jobs/{id}/discard      -> job (hidden from the list; ComfyUI untouched)
 
 job = {"id","status","queue_position"?,"error"?,"path","library_id","template",
@@ -737,7 +746,8 @@ POST   /image/tags/bulk  (many files, one transaction: { file_names, add: [names
 GET /image/versions?path=...&library=...   (path of the original or any version ->
                                             { original:{path,library_id,hash}, versions:[{path,
                                             library_id,hash,kind,source,created_at,references,
-                                            width,height}], display_hash })
+                                            width,height}], clips:[same shape, kind animated],
+                                            display_hash })
 POST /enhance ...                          (Enhance on demand; see "Enhance on demand")
 PUT /image/versions/display                (body { path, display_hash|null, library? }; global choice)
 //   /photos hides versions behind their original (include_versions=true lists them) and adds