refactor: remove unused bd pin/unpin/hook commands (bd-x0zl)

Analysis found these commands are dead code:
- gt never calls `bd pin` - uses `bd update --status=pinned` instead
- Beads.Pin() wrapper exists but is never called
- bd hook functionality duplicated by gt mol status
- Code comment says "pinned field is cosmetic for bd hook visibility"

Removed:
- cmd/bd/pin.go
- cmd/bd/unpin.go
- cmd/bd/hook.go

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor/legacy_test.go

@@ -410,6 +410,49 @@ func TestCheckLegacyJSONLConfig(t *testing.T) {
 	}
 }
 
+func TestCheckDatabaseConfig_IgnoresSystemJSONLs(t *testing.T) {
+	tmpDir := t.TempDir()
+	beadsDir := filepath.Join(tmpDir, ".beads")
+	if err := os.Mkdir(beadsDir, 0750); err != nil {
+		t.Fatal(err)
+	}
+
+	// Configure issues.jsonl, but only create interactions.jsonl.
+	metadataPath := filepath.Join(beadsDir, "metadata.json")
+	if err := os.WriteFile(metadataPath, []byte(`{"database":"beads.db","jsonl_export":"issues.jsonl"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(beadsDir, "interactions.jsonl"), []byte(`{"id":"x"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	check := CheckDatabaseConfig(tmpDir)
+	if check.Status != "ok" {
+		t.Fatalf("expected ok, got %s: %s\n%s", check.Status, check.Message, check.Detail)
+	}
+}
+
+func TestCheckDatabaseConfig_SystemJSONLExportIsError(t *testing.T) {
+	tmpDir := t.TempDir()
+	beadsDir := filepath.Join(tmpDir, ".beads")
+	if err := os.Mkdir(beadsDir, 0750); err != nil {
+		t.Fatal(err)
+	}
+
+	metadataPath := filepath.Join(beadsDir, "metadata.json")
+	if err := os.WriteFile(metadataPath, []byte(`{"database":"beads.db","jsonl_export":"interactions.jsonl"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(beadsDir, "interactions.jsonl"), []byte(`{"id":"x"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	check := CheckDatabaseConfig(tmpDir)
+	if check.Status != "error" {
+		t.Fatalf("expected error, got %s: %s", check.Status, check.Message)
+	}
+}
+
 func TestCheckFreshClone(t *testing.T) {
 	tests := []struct {
 		name           string