feat(ui): feature-parity context menu — Snap Overrides, transparent Pan/Zoom, ARC keyword flow

The command menu now follows the commercial solutions' layout row for row: Enter, Cancel,
Recent Input ▸, the command's keywords, Snap Overrides ▸ (every object snap
with its glyph, Mid Between 2 Points, None, Osnap Settings…), then Pan and
Zoom. Pan / Zoom run transparently while a command is active ('PAN,
'ZOOM …): navigation modes leave the command untouched and an interactive
ZOOM Window parks it and resumes it afterwards. Rows carry an icon gutter
so labels align; the Enter row shows a default value ("<0.5000>") as its
hint instead of a second finish row.

ARC gets the commercial solutions' prompt flow with all keywords: start [Center], second
point [Center/End], end; after Center: end [Angle/chord Length]; after
End: center [Angle/Direction/Radius]; Enter continues tangent. The
previous default (Center/Start/End with method codes) stays as ARC_CSE.

Object snaps gain a one-shot "None" override. New strings in all locales.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/update/mod.rs

@@ -754,6 +754,14 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::SnapOverrideNone => {
+                self.snap_override_popup = None;
+                self.snapper.set_override_none();
+                self.command_line
+                    .push_info(crate::t!("Snap override: None (next pick only).").as_ref());
+                Task::none()
+            }
+
             Message::SnapOverrideMtp => {
                 self.snap_override_popup = None;
                 self.tabs[self.active_tab]