Bridge Coach memory brief with project metrics summaries.

Add Performance Summary block to memory brief, document metrics synthesis in
agent-coach, and add e2e and CLI tests for qualitative plus quantitative briefs.

tests/test_metrics_cli.py

@@ -114,6 +114,30 @@ class TestMetricsCli:
         assert metrics_dir.exists()
         assert (metrics_dir / "executions.jsonl").exists()
 
+    def test_memory_brief_includes_performance_summary(
+        self, runner: CliRunner, project_dir: Path
+    ):
+        target = str(project_dir)
+        runner.invoke(cli, ["memory", "init", "tdd-workflow", "--target", target])
+        runner.invoke(
+            cli,
+            [
+                "metrics",
+                "record",
+                "tdd-workflow",
+                "--target",
+                target,
+                "--success",
+                "--quality",
+                "0.9",
+            ],
+        )
+
+        result = runner.invoke(cli, ["memory", "brief", "tdd-workflow", "--target", target])
+        assert result.exit_code == 0
+        assert "## Performance Summary" in result.output
+        assert "Success rate: 100.0%" in result.output
+
     def test_memory_init_no_metrics_flag(self, runner: CliRunner, project_dir: Path):
         result = runner.invoke(
             cli,