Video frames from bytes, not from a CORS player; pager clips load plainly again

Regression from 6488806: pager clips were loaded crossorigin so their
frame could be kept, and on a phone the large clip's slide went black.
Some hosts (Primal's R2 bucket) send CORS headers only to a request with
an Origin and don't Vary on it, so a copy the browser cached from a plain
player load answers a later CORS load without them, and it fails. The
same thing made the size probe fail for any clip that had played in the
feed.

- Pager clips load plainly again; the still under a tap-to-play cover is
  restored on every return.
- The probe (and its HEAD) go past the browser cache (no-store).
- A clip's frame is now made from bytes: the opening of the file (index
  plus about 1 MB, no-store) decoded from a blob and kept as a JPEG —
  for tiles and as the pager's poster. No CORS player anywhere. Files
  whose index trails, or hosts whose bytes can't be read, keep the plain
  player still (shown, not kept).
- Kept frames are 480 px wide (were 270) and capped at 600.
- Probe failures are stored as failedAt, so earlier failures are asked
  again at once.
- Test: an R2-style host, its clip cached by a plain load first, is
  still measured and its frame kept (failed before this change).

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01ULQZS9MQa6iAsXnrJUD9Du

0 files changed, 0 insertions, 0 deletions