fix(clip): a clip is held to its owner's storage cap, and its limits and failures say the server's truth

- The cut file is measured against what its owner has left, for a YouTube range (whose fetch never
  reads yt-dlp's size ceiling) and for a Plex clip (which fetches nothing), before the fetch and
  again before it is placed; a refusal leaves the asset pending for a Retry.
- A silent Plex file is cut silent; a file the probe cannot read says so.
- A second job on a failed or renamed clip gets the same YouTube diagnosis and the fetched title.
- The "too long" refusal names the server's cap; a contract test holds the client's copies of the
  clip limits to clip.py; the shipped player clients are pinned against the installed yt-dlp.
- One HDR transfer set and one rating_key lookup; job status words from JobStatus; the display-name
  guard sees subscript writes and the clip route; stale comments and types follow the clip job.

backend/app/models.py

@@ -933,8 +933,9 @@ class DownloadJob(Base, TimestampMixin, UpdatedAtMixin):
     )
     source_kind: Mapped[str] = mapped_column(String(16))  # "youtube" | "url"
     source_ref: Mapped[str] = mapped_column(String(512))
-    # "download" (default), "edit" (a per-user trim/crop derivative of another job) or "upload" (a
-    # user's own file, converted by the worker when it is not phone-safe — see `downloads.upload`).
+    # "download" (default), "edit" (a per-user trim/crop derivative of another job), "upload" (a
+    # user's own file, converted by the worker when it is not phone-safe — see `downloads.upload`) or
+    # "clip" (a range cut straight from a YouTube video or a Plex item — see `downloads.clip`).
     job_kind: Mapped[str] = mapped_column(String(16), default="download", server_default="download")
     # For edit jobs: the parent download this clip is cut from (SET NULL if the parent is deleted).
     source_job_id: Mapped[int | None] = mapped_column(
@@ -943,7 +944,9 @@ class DownloadJob(Base, TimestampMixin, UpdatedAtMixin):
     source_asset_id: Mapped[int | None] = mapped_column(
         ForeignKey("media_assets.id", ondelete="SET NULL")
     )
-    # For edit jobs: the trim/crop recipe {trim?:{start_s,end_s}, crop?:{x,y,w,h}}.
+    # For edit jobs: the trim/crop recipe {trim?:{start_s,end_s}, crop?:{x,y,w,h}} in pixels. For clip
+    # jobs: the clip spec {source, ref, start_s, end_s, audio_track?, crop?:{x,y,w,h,aspect}}, its crop
+    # in fractions of the box it was drawn in (`downloads.clip.normalize`).
     edit_spec: Mapped[dict | None] = mapped_column(JSON)
     profile_id: Mapped[int | None] = mapped_column(
         ForeignKey("download_profiles.id", ondelete="SET NULL")