Reconcile durable worker lifecycles

[akgohain]

Summary

Makes durable model operations represent the worker lifecycle rather than only submission acceptance.

• Accepted training and inference commands remain running.
• Adds an authenticated, generic reconciliation endpoint for correlated PyTC runtime snapshots.
• Strict workflow/command/run correlation prevents process-global worker state from completing the wrong operation.
• Terminal snapshots idempotently produce succeeded, failed, or cancelled operation state and matching workflow/model-run evidence.
• Worker snapshots retain canonical correlators, exit state, errors, and discovered artifacts for both training and inference.

Scope boundary

Reconciliation is an explicit backend primitive in this layer. The next stacked layer will own cancellation transport, polling/supervision, and restart recovery.

Verification

• Full backend suite: 340 passed, 9 subtests passed
• Focused runtime/operation/artifact/worker suites: 70 passed, 9 subtests passed
• Black and git diff --check passed.