Implement MetricsStore for project-scoped agent metrics.

Add ADR-004 storage layer with append-only executions, summary
regeneration, idempotency keys, and retention pruning. Wire memory init
to scaffold .kaizen/metrics/ by default and add unit tests.

src/kaizen_agentic/cli.py

@@ -10,6 +10,7 @@ from typing import List, Optional
 
 from .registry import AgentRegistry, AgentCategory
 from .installer import AgentInstaller, ProjectInitializer, InstallationConfig
+from .metrics import MetricsStore
 
 
 def safe_cli_wrapper():
@@ -781,7 +782,12 @@ def memory_show(agent_name: str, target: str):
 @memory.command("init")
 @click.argument("agent_name")
 @click.option("--target", "-t", default=".", help="Project root (default: current)")
-def memory_init(agent_name: str, target: str):
+@click.option(
+    "--no-metrics",
+    is_flag=True,
+    help="Skip scaffolding .kaizen/metrics/<agent>/ (default: create metrics dir)",
+)
+def memory_init(agent_name: str, target: str, no_metrics: bool):
     """Scaffold an empty memory file for an agent."""
     memory_path = _memory_path(target, agent_name)
 
@@ -820,6 +826,10 @@ session_count: 0
     memory_path.write_text(content)
     click.echo(f"Initialized memory for '{agent_name}': {memory_path}")
 
+    if not no_metrics:
+        metrics_dir = MetricsStore(Path(target), agent_name).scaffold()
+        click.echo(f"Initialized metrics for '{agent_name}': {metrics_dir}")
+
     # For agents with protocols, note the protocol location
     registry = _get_registry()
     protocols_dir = registry.agents_dir / "protocols" / agent_name