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>

workplans/kaizen-agentic-WP-0002-agency-framework.md

@@ -140,14 +140,14 @@ kaizen-agentic memory clear <agent>     # Wipe memory (with confirmation)
 **Memory convention and tooling**
 - [x] T07 — Write ADR: project memory convention (file location, structure, lifecycle)
 - [x] T08 — Implement `memory` CLI command group (show, init, brief, clear)
-- [ ] T09 — Add session-start and session-close protocol sections to agent template /
+- [x] T09 — Add session-start and session-close protocol sections to agent template /
              contributor guide
 
 **Agent definition updates**
-- [ ] T10 — Add session-start and session-close protocol blocks to all existing
+- [x] T10 — Add session-start and session-close protocol blocks to all existing
              agents that do session-bound work (project-management, tdd-workflow,
              requirements-engineering, scope-analyst, sys-medic)
-- [ ] T11 — Update agent YAML frontmatter schema to include optional
+- [x] T11 — Update agent YAML frontmatter schema to include optional
              `memory: enabled|disabled` field (default: enabled)
 
 **Coaching meta-agent**