feat(memory): add memory CLI command group and project memory ADRs

- Add docs/adr/ADR-001-workplan-convention.md (formalises existing convention)
- Add docs/adr/ADR-002-project-memory-convention.md (file location, structure,
  session protocols, opt-out, CLI interface)
- Implement `kaizen-agentic memory` command group: show, init, brief, clear
  - Memory stored at .kaizen/agents/<name>/memory.md in project root
  - `init` scaffolds the standard memory template with YAML frontmatter
  - `brief` lists all agent memories + note that coach synthesis is pending T13
  - `clear` deletes with confirmation prompt

WP-0002 T07 and T08 done.

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

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

@@ -138,8 +138,8 @@ kaizen-agentic memory clear <agent>     # Wipe memory (with confirmation)
 ### Tasks
 
 **Memory convention and tooling**
-- [ ] T07 — Write ADR: project memory convention (file location, structure, lifecycle)
-- [ ] T08 — Implement `memory` CLI command group (show, init, brief, clear)
+- [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 /
              contributor guide