learn: add reviewer constraints from PR #2954

[strandly-the-agent]

Appends a new ## Learned Constraints section to strands-command/agent-sops/task-reviewer.sop.md with two durable, generalizable review rules learned from the lifecycle of strands-agents/harness-sdk#2954 and its root-cause issue #2918. No existing section is modified.

1. For lock/concurrency fixes: release a lock only by the path that proved it acquired it (mirror the acquire result, as tools/_caller.py does), never via a re-derived mode/config proxy; flag ownership-named fields that aren't true in every mode.
2. For bugfixes linked to a root-cause issue: confirm the change resolves the documented root cause or that a tracking issue exists for the remainder, rather than treating a symptom fix as fully closing the bug.

Run: learning-run-pr2954