fix(onboard): use AGENTS.md template instead of AGENT.md (#931)

* fix(onboard): use AGENTS.md workspace template

* test(onboard): move AGENTS template regression test to new package

cmd/picoclaw/internal/onboard/helpers_test.go

@@ -0,0 +1,25 @@
+package onboard
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestCopyEmbeddedToTargetUsesAgentsMarkdown(t *testing.T) {
+	targetDir := t.TempDir()
+
+	if err := copyEmbeddedToTarget(targetDir); err != nil {
+		t.Fatalf("copyEmbeddedToTarget() error = %v", err)
+	}
+
+	agentsPath := filepath.Join(targetDir, "AGENTS.md")
+	if _, err := os.Stat(agentsPath); err != nil {
+		t.Fatalf("expected %s to exist: %v", agentsPath, err)
+	}
+
+	legacyPath := filepath.Join(targetDir, "AGENT.md")
+	if _, err := os.Stat(legacyPath); !os.IsNotExist(err) {
+		t.Fatalf("expected legacy file %s to be absent, got err=%v", legacyPath, err)
+	}
+}