feat: integrate Grafana dashboards into BOC DashboardPage

- Add Infrastructure Health section with CPU/Memory/Disk panels
- Add Service Status section with PM2/Docker panels
- Create GrafanaPanel component for iframe embedding
- Build passes successfully

backend/handlers/crm.go

@@ -18,13 +18,25 @@ func NewCRMHandler(db *sql.DB) *CRMHandler {
 	return &CRMHandler{DB: db}
 }
 
+// NullString is a sql.NullString that marshals to a plain string in JSON
+type NullString struct {
+	sql.NullString
+}
+
+func (ns NullString) MarshalJSON() ([]byte, error) {
+	if ns.Valid {
+		return json.Marshal(ns.String)
+	}
+	return json.Marshal("")
+}
+
 type Customer struct {
 	ID        string     `json:"id"`
 	Name      string     `json:"name"`
 	Email     string     `json:"email"`
-	Phone     string     `json:"phone"`
+	Phone     NullString `json:"phone"`
 	Company   string     `json:"company"`
-	OrgNumber string     `json:"org_number"`
+	OrgNumber NullString `json:"org_number"`
 	Status    string     `json:"status"`
 	Source    string     `json:"source"`
 	Tags      []string   `json:"tags"`