Update AGENTS.md files across multiple modules to standardize task status update instructions and introduce a new document for Secret Leak Detection operations.

- Modified task status update instructions in AGENTS.md files to refer to corresponding sprint files as `/docs/implplan/SPRINT_*.md` instead of `docs/implplan/SPRINTS.md`.
- Added a comprehensive document for Secret Leak Detection operations detailing scope, prerequisites, rule bundle lifecycle, enabling the analyzer, policy patterns, observability, troubleshooting, and references.

src/Policy/StellaOps.Policy.Engine/AGENTS.md

@@ -14,7 +14,7 @@ Stand up the Policy Engine runtime host that evaluates organization policies aga
 - Keep endpoints deterministic, cancellation-aware, and tenant-scoped.
 - Only Policy Engine identity performs writes to effective findings.
 - Coordinate with Concelier/Excititor/Scheduler guilds for linkset joins and orchestration inputs.
-- Update `TASKS.md`, `../../docs/implplan/SPRINTS.md` when status changes.
+- Update `TASKS.md`, `/docs/implplan/SPRINT_*.md` when status changes.
 - Maintain compliance checklists and schema docs alongside code updates.
 
 ## Required Reading
@@ -22,7 +22,7 @@ Stand up the Policy Engine runtime host that evaluates organization policies aga
 - `docs/modules/platform/architecture-overview.md`
 
 ## Working Agreement
-- 1. Update task status to `DOING`/`DONE` in both `docs/implplan/SPRINTS.md` and the local `TASKS.md` when you start or finish work.
+- 1. Update task status to `DOING`/`DONE` in both correspoding sprint file `/docs/implplan/SPRINT_*.md` and the local `TASKS.md` when you start or finish work.
 - 2. Review this charter and the Required Reading documents before coding; confirm prerequisites are met.
 - 3. Keep changes deterministic (stable ordering, timestamps, hashes) and align with offline/air-gap expectations.
 - 4. Coordinate doc updates, tests, and cross-guild communication whenever contracts or workflows change.