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.

docs/modules/vex-lens/AGENTS.md

@@ -11,7 +11,7 @@ VEX Lens computes deterministic consensus across conflicting VEX statements whil
 
 ## How to get started
 1. Review ./architecture.md for consensus algorithm, trust model, and export contracts.
-2. Open ../../implplan/SPRINTS.md and locate stories for this component.
+2. Open sprint file `/docs/implplan/SPRINT_*.md` and locate stories for this component.
 3. Check ./TASKS.md and update status before/after work.
 4. Read README/architecture for design context and update as the implementation evolves.
 
@@ -28,7 +28,7 @@ VEX Lens computes deterministic consensus across conflicting VEX statements whil
 - `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.