Add lazy Auto Review detail retrieval

[shiny-code-bot]

Summary

Add lazy detail retrieval for Auto Review runs so the per-turn ledger stays small while full findings remain accessible when useful.

Scope

• Add a read-only detail operation/tool by run_id and optional finding_id.
• Read from durable output sidecars.
• Bound/truncate returned detail and report explicit missing-detail errors.
• Do not let detail retrieval mutate run disposition.

Acceptance Criteria

• Details can be retrieved by stable run/finding id.
• Detail output is bounded/truncated with clear metadata.
• Missing or unavailable details return an explicit error.
• Default ledger does not include full review JSON or raw diffs.
• Tests cover detail lookup, truncation, and missing sidecars.

Relationships

Parent: #324
Depends on: #325, #327

Finish Line

The assistant can retrieve bounded Auto Review result/finding details by stable run or finding id, while default turn context remains compact and read-only.