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-tdd-workflow.md

@@ -357,3 +357,18 @@ Remember: The goal is to build software incrementally using the proven TDD8 cycl
 **ISSUE-TEST-RED-GREEN-REFACTOR-DOCUMENT-REFINE-PUBLISH**
 
 The comprehensive 8-step development methodology that transforms requirements into production-ready, well-tested, documented functionality while maintaining code quality and project momentum through intelligent sidequest management.
+
+---
+
+## Session Start
+
+1. Check for `.kaizen/agents/tdd-workflow/memory.md` in the project root.
+2. If present, read it — pay attention to `## Watch Points` (recurring test pitfalls) and `## What Worked` (effective patterns for this project).
+3. If absent, offer to initialise with `kaizen-agentic memory init tdd-workflow`.
+
+## Session Close
+
+1. Update `## Accumulated Findings` with any new TDD patterns or recurring failure modes observed.
+2. Update `## What Worked` and `## Watch Points` as needed.
+3. Append one line to `## Session Log`: `YYYY-MM-DD · <issue or feature> · <outcome>`.
+4. Bump `last_updated` to today and increment `session_count`.