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>

CONTRIBUTING.md

@@ -71,6 +71,40 @@ For contributing new agents or improving existing ones:
 - Define explicit scope and authority boundaries
 - Follow existing agent patterns in `agents/` directory
 
+#### YAML frontmatter schema
+
+```yaml
+---
+name: <agent-name>
+description: <one-line description>
+category: testing | quality | process | infrastructure | release | docs | support | meta
+memory: enabled  # optional; default enabled. Set to disabled for stateless utility agents
+---
+```
+
+#### Session-start protocol (for session-bound agents)
+
+Agents that do ongoing work across sessions should include a session-start block:
+
+1. Check for `.kaizen/agents/<name>/memory.md` in the project root
+2. If present, read it and acknowledge relevant context in the opening brief
+3. Optionally invoke `kaizen-agentic memory brief <name>` for cross-agent orientation
+
+Include this block in the agent prompt under a `## Session Start` heading.
+
+#### Session-close protocol (for session-bound agents)
+
+At the end of each session the agent should:
+
+1. Update `## Accumulated Findings`, `## What Worked`, `## Watch Points` as needed
+2. Append one line to `## Session Log` (format: `YYYY-MM-DD · <summary> · <outcome>`)
+3. Bump `last_updated` and `session_count` in the frontmatter
+
+Include this block in the agent prompt under a `## Session Close` heading.
+
+Agents for which session state is irrelevant (e.g. `keepaTodofile`, `keepaChangelog`)
+should set `memory: disabled` in their frontmatter and omit these sections.
+
 ## Types of Contributions
 
 We welcome various types of contributions: