Preserve durable Tinker training state

[lluisinthedesert]

Why

Final Tinker SFT artifacts were saved with a one-hour TTL. A Cedar checkpoint expired before serving qualification, forcing a full retrain and making the apparent model failure indistinguishable from checkpoint lifecycle failure.

What

• save a non-expiring resumable training state before evaluation
• keep sampler weights bounded to 24 hours
• receipt-bind both paths and TTL policies
• update the deterministic contract test

Verification

• npm run build
• node --test tests/tinker-sft.test.mjs (7/7)

No provider calls or holdout access were used for this change.