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/architect/MEMORY.md

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+# Architect — Memory
+
+This role's own accumulated context: recurring review findings, patterns in where scope tends
+to creep, and past technical judgment calls along with the reasoning behind them. Not
+automatically shared with other roles — see `../../MEMORY.md` on the two-tier memory system.
+Promote anything company-wide to `../../memory/architecture-memory.md` instead of leaving it
+siloed here.
+
+## Recurring review findings
+
+*None recorded yet.* When the same category of issue shows up across multiple PRs (e.g. a
+pattern of scope creep in one project, or a recurring gap in test coverage), record it here so
+it's caught in review earlier, and consider whether it means `../../CODING_STANDARDS.md` needs
+an update.
+
+## Technical judgment calls
+
+*None recorded yet.*
+
+```
+### YYYY-MM-DD — <short title>
+<the call made, and the situation it responded to>
+**Reasoning:** <why this call, over the alternatives>
+```
+
+## Disagreements resolved
+
+*None recorded yet.* A log of disagreements adjudicated, so a similar future disagreement can
+be resolved consistently rather than re-litigated from scratch — and so a pattern of recurring
+disagreement in one area surfaces as a signal worth acting on.
+
+## Format for new entries
+
+```
+### YYYY-MM-DD — <short title>
+
+<the observation>
+
+**Why it matters:** <what this changes about how you review/decide going forward>
+```