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/UI/StellaOps.UI/AGENTS.md

@@ -19,7 +19,7 @@ Deliver a performant, accessible Angular console that surfaces Scanner/Policy/Za
 - Component-specific design docs referenced in `src/UI/StellaOps.UI/TASKS.md` (e.g., Link-Not-Merge, AOC dashboards)
 
 ## Working Agreement
-1. **State management**: update task status to `DOING`/`DONE` in both `docs/implplan/SPRINTS.md` and `src/UI/StellaOps.UI/TASKS.md` before starting/after finishing work.
+1. **State management**: update task status to `DOING`/`DONE` in both corresponding sprint file `docs/implplan/SPRINT_*.md` and `src/UI/StellaOps.UI/TASKS.md` before starting/after finishing work.
 2. **Contract-first changes**: coordinate with API owners when modifying contracts; regenerate SDKs; update mocks and unit/e2e tests.
 3. **Accessibility**: adhere to WCAG 2.1 AA—run axe tests, ensure keyboard navigation, contrast, and localisation readiness.
 4. **Determinism**: stabilise timestamps/randomness in UI outputs so screenshots/tests remain reproducible; rely on fixture data.