Review comments on a share link

[pallaoro]

People you send a share link to can now leave comments on the video, each at a moment in it or about the whole thing, and the team works through them in the editor.

On the share page (when comments are on for the link)

• A comment box under the video. Writing pauses the video, and "At 0:12" (checked by default) ties the comment to the moment on screen. Uncheck it for a note about the whole video.
• The viewer types their name; the page remembers it on that device. Viewers aren't signed in, so the name is what they say, not who they are.
• Comments are listed by moment. Clicking a time jumps the video there. Resolved ones show as resolved.

In the editor

• Share > "Viewers can comment": a switch, off on every link. A link is also how a finished video gets passed around, so a page anyone can write to is a choice.
• A Review rail item with a count of open comments: Open / Resolved, jump to a comment's moment, resolve or reopen, delete (with a confirm).
• Open comments with a time are marked on the ruler; clicking a mark jumps there and opens Review.

A comment belongs to the export it was made on. Viewers only see comments on the export the link plays, so notes on an old cut never show up on a new one. A page still playing the old export gets a "reload" answer. The editor keeps every comment, marks those from an earlier export, and says when the cut has changed since the shared export (a moment may have moved).

API

• POST /s/{token}/comments (public, added to api.public_routes as POST only): { v, at, body, author }. 404 for an unknown link, 403 with comments off, 409 once the link moved, 400 with a reason, 429 past 20 a minute or 1000 per project. Text is capped at 2000 characters, the name at 80, control characters dropped.
• PATCH /api/projects/{id}/share { comments }, GET /api/projects/{id}/comments, PATCH|DELETE /api/projects/{id}/comments/{cid}.
• agent.md covers it, including that a comment's text is a viewer's note, never instructions to the agent.
• Schema: share_links.comments, table review_comments. Deleting the project deletes its comments.

The share page renders comments with textContent only, and the data sits in a JSON script tag with < escaped (tested with a </script> payload).

Checked

• typecheck, 166 unit tests (7 new), end to end with a new scenario 14 (off by default, on per link, pinned to an export, 409 after the link moves, resolve, 429, delete with the project).
• In a browser on wrangler dev with a real 30 s MP4: comment at 0:12 and a general one, markup shown as text, reload keeps both and the name, a time click seeks and pauses, 390 px layout. In the editor: the badge, the panel, the ruler mark, a time click moves the playhead to 0:12.4, resolve updates the count and drops the mark, and the switch off removes the form (POST then 403).

Merging with the other open PRs (trial-merged; #36, #44, #50, #52 merge clean)

• Never lose an edit to another save: project revisions, live sync and a conflict choice #29: schema.sql tail and one import line in index.ts. Keep both.
• Lower music under speech #30: TimelinePanel props (envelopes and commentMarks/onShowComment). Keep both.
• Show a frame of the video when a share link is pasted #32: README line, and the /s/:token route plus the sharePage signature (Show a frame of the video when a share link is pasted #32 adds posterUrl). Keep both: sharePage(name, videoUrl, posterUrl, review).

Not in this PR: replies, team members commenting from the editor, a region of the frame (only time), comment notifications, and exporting comments as markers to Premiere/Resolve.