Add bounded snapshot-consistent agent replay

[dispatch-developer]

Summary

• add a delegated-agent replay endpoint bound to owner, conversation, turn, and agent JWT claims
• read the atomic turn-start boundary and ordered transcript from one repeatable-read snapshot
• enforce configured item/serialized-byte limits with typed context-limit errors
• allow only historical user input_text and assistant output_text messages, rejecting media and unresolved Threadmark URIs
• preserve ordinary owner replay behavior and document the Bonsai text-only contract and configuration

Tests

• added unit coverage for delegated scope isolation, item/byte limit boundaries, configured field stripping, deterministic order, and unsupported content
• not run locally because the provided environment does not include cargo or rustfmt

Closes #5

[dispatch-reviewer]

CI is failing for this revision: cargo fmt --check reports formatting changes needed in src/config.rs, src/error.rs, and src/store.rs. Because formatting failed, Clippy and the test suite were skipped. Please run cargo fmt and rerun the full CI.

[dispatch-reviewer]

CI remains failing. Please address the reviewer feedback and rerun CI.

[dispatch-reviewer]

Reviewed the bounded delegated-agent replay flow, authorization scope checks, snapshot query, projection limits, and error handling. CI passed (fmt, clippy, and tests).