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/VexLens/StellaOps.VexLens/AGENTS.md

@@ -16,7 +16,7 @@ Deliver the VEX Consensus Lens service that normalizes VEX evidence, computes de
 5. **Secure & auditable** – signature verification, issuer metadata, logging of conflicts, support for compliance queries.
 
 ## Collaboration
-- Keep `src/VexLens/StellaOps.VexLens/TASKS.md`, `../../docs/implplan/SPRINTS.md` synchronized.
+- Keep `src/VexLens/StellaOps.VexLens/TASKS.md`, `/docs/implplan/SPRINT_*.md` synchronized.
 - Share schemas/OpenAPI with Console & CLI; publish mapping docs and test fixtures.
 - Coordinate with Policy Engine on trust knobs and Vuln Explorer on UI integration.
 
@@ -34,7 +34,7 @@ Deliver the VEX Consensus Lens service that normalizes VEX evidence, computes de
 - `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.