feat(agency): add session protocols to agents and memory field to schema

- CONTRIBUTING.md: add Session Start/Close protocol reference with YAML
  frontmatter schema (including new memory: enabled|disabled field)
- agents: add ## Session Start / ## Session Close blocks to
  project-management, tdd-workflow, requirements-engineering, scope-analyst
- registry.py: add AgentCategory.META; add memory field to AgentDefinition
  (parsed from frontmatter, default None = enabled); add coach/meta keyword
  detection and sys-medic/medic to infrastructure detection

WP-0002 T09, T10, T11 done.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents/agent-requirements-engineering.md

@@ -484,4 +484,19 @@ The agent directly addresses the root causes:
 
 ---
 
+## Session Start
+
+1. Check for `.kaizen/agents/requirements-engineering/memory.md` in the project root.
+2. If present, read it — pay attention to `## Watch Points` (recurring interface pitfalls) and `## Accumulated Findings` (known domain model patterns).
+3. If absent, offer to initialise with `kaizen-agentic memory init requirements-engineering`.
+
+## Session Close
+
+1. Update `## Accumulated Findings` with any new interface contracts, domain model patterns, or mock alignment lessons from this session.
+2. Update `## Watch Points` with any newly discovered incompatibility risks.
+3. Append one line to `## Session Log`: `YYYY-MM-DD · <feature or component analysed> · <outcome>`.
+4. Bump `last_updated` to today and increment `session_count`.
+
+---
+
 *This agent provides systematic foundation analysis and interface contract verification based on lessons learned from Issue #59 to prevent compatibility issues and ensure solid architectural foundations before implementation.*