Feat: viewport display lock, extended properties, VPLAYER and VPORTS commands

- Enforce status.locked in pan_active_viewport and zoom_active_viewport:
  locked viewports now reject pan/zoom inputs entirely
- Add perspective, render_mode, shade_plot_mode, hide_plot, ucs_icon_visible
  fields to the viewport property panel with appropriate pickers/toggles
- Add VPORTS command: lists all user viewports in the current layout
  (id, size, position, scale, on/locked state) in the command line
- Add VPLAYER command: per-viewport layer freeze/thaw from the command line
  (F <layer> to freeze, T <layer> to thaw, Enter to exit)
- Add CmdResult::VpLayerUpdate variant and its handler in apply_cmd_result

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/layout/mod.rs

@@ -2,6 +2,7 @@
 // This tab is only shown when the active layout is not "Model".
 
 pub mod mview;
+pub mod vplayer;
 
 use crate::modules::{CadModule, IconKind, ModuleEvent, RibbonGroup, ToolDef};