v19s: WebChain real-site trajectories, format v5, webgym x7 + DAgger, harness fixes; replaces v17s

Single model: v17s (suite A 85 %, suite B 100 %, webgym 47 %); replaces v15s (kept in history)

v14s checkpoint, held-out suite B (100 %), harness fixes, webgym + sub-goal data pipeline, DAgger leak correction

code: rollouts, teacher eval, corrected suite checks

laya-browser v10 / v10s: laya fine-tuned as a browser-agent decision head + code + results