refactor: simplify db and cmd flags, reduce code duplication

- Abstract property flags into addPropertyFlags in cmd/root.go and apply to commands
- Remove unused GetUserByUsername from db.go (it's redundant with service.resolveUserIDByName)
- Use configured user in WithMentions directly in inbox command
- Refactor resolve methods in node_service_sqlite.go to reduce duplication

cmd/root.go

@@ -76,3 +76,10 @@ func transformArgs(args []string) []string {
 func init() {
 	rootCmd.PersistentFlags().BoolVar(&jsonFlag, "json", false, "")
 }
+
+func addPropertyFlags(cmd *cobra.Command) {
+	cmd.Flags().String("type", "", "node type")
+	cmd.Flags().String("status", "", "node status")
+	cmd.Flags().String("prio", "", "node priority")
+	cmd.Flags().String("namespace", "", "node namespace")
+}