fix(watch): avoid reloading full recordings while saving

Retain only successfully encoded sample timing for final statistics and
read manifest metadata for the Watch saved receipt. Preserve retry, loss
accounting and immutable masters.

Matched physical-data replay on Mac reduced finalization from1.52s to0.05s
and peakRSS from236MB to93MB, with identical rows and statistics.
43 core,7 Watch and10 iPhone checks pass; independent review has no
blockers. Build16 is signed and ready; physical installation and save
verification remain pending a dropped device connection.