feat(review): flag handles in the review player (metadata only)

Renders run 8 frames past the cut at each end. Directors were flagging
glitches in unfixed handles as shot problems, so the player now marks
them — without trimming or burning anything into the EXRs/MOV/MP4.

- Version.handleHead/handleTail/pictureStartFrame, Export.handleHead/
  handleTail; migration backfills pipeline exports and their preview
  versions from the manifest's handleFrames (else 8)
- AE panel: "Includes handles [8] frames each end" -> manifest.review;
  older manifests fall back to source.handleFrames
- finalize copies handles onto the Version; worker 1.6.4 reports the
  head slate length (pictureStartSeconds), else the player infers it
  as MP4 frames - EXR frameCount
- Player: hatched HANDLE / SLATE regions and cut marks on the timeline,
  "HEAD/TAIL HANDLE · NOT IN EDIT" overlay on handle frames, HANDLE badge
  on notes, "Edit range only" toggle (default on in the client portal)
- Staff Handles editor on the review page for manual uploads/corrections

Also fixes two player bugs found while testing: timeToFrame floored
float error (every seek landed a frame early), and J/reverse never ran
(the keyboard effect's cleanup stopped it on the next render).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/frame-utils.ts

@@ -9,9 +9,17 @@ export function frameToTime(frame: number, fps: number): number {
   return frame / fps;
 }
 
+/**
+ * Tolerance (in frames) for float error at a frame boundary. Seeking to
+ * frameToTime(4, 24) = 0.1666… reads back as 3.9999… frames; without this it
+ * floors to frame 3, so every seek landed one frame early. Far smaller than
+ * any real position inside a frame.
+ */
+const FRAME_EPSILON = 1e-3;
+
 /** Convert video currentTime to frame number (0-based) */
 export function timeToFrame(time: number, fps: number): number {
-  return Math.floor(time * fps);
+  return Math.floor(time * fps + FRAME_EPSILON);
 }
 
 /** Format a frame number as a timecode string: MM:SS:FF */