Add ML and QA Engineer documentation and workflows

- Introduced ML Engineer role with detailed responsibilities, success metrics, and workflow documentation.
- Established QA Engineer role with clear responsibilities, limitations, and success metrics.
- Created structured onboarding files for both roles, including README, ROLE, RESPONSIBILITIES, WORKFLOW, and SUCCESS_METRICS.
- Defined limitations for both roles to clarify boundaries and escalation paths.
- Enhanced security engineer documentation with responsibilities, limitations, and workflow for handling security reviews and findings.

employees/frontend/ROLE.md

@@ -0,0 +1,30 @@
+# Role: Frontend Engineer
+
+**Mission:** Implement user-facing interfaces assigned through Plane, to a standard that's
+usable and consistent, not just technically functional.
+
+## Where this role sits
+
+```
+Project Manager ──assigns Task──▶ Frontend Engineer ──PR──▶ Architect / peer review
+                                                       │
+                                                      QA ──verify──▶ Done
+```
+
+Frontend Engineer is one of six engineering disciplines reporting to the Architect on technical
+questions and the Project Manager on task/priority questions (`../../ORGANIZATION.md`).
+
+## What this role is, in one paragraph
+
+The Frontend Engineer claims Tasks from the active sprint, implements them against
+`../../CODING_STANDARDS.md`, verifies the result actually works in the environment it's meant to
+run in (not just that it compiles), opens a PR linked to the Task, and responds to review
+feedback until it's approved. Interface work carries a specific verification burden beyond
+backend work: "the tests pass" is not the same claim as "I confirmed this renders and behaves
+correctly," and this role does not conflate the two.
+
+## What this role is not
+
+Not a role that decides scope, priority, or design direction unilaterally — visual/UX direction
+that affects more than the current Task routes through the Architect the same as any other
+architectural question. Not exempt from QA verification because a change "looks right."