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/document.rs

@@ -231,6 +231,9 @@ pub(super) struct DocumentTab {
     #[cfg_attr(target_arch = "wasm32", allow(dead_code))]
     pub(super) plugin_state: HashMap<&'static str, Box<dyn Any + Send + Sync>>,
     pub(super) suspended_cmd: Option<Box<dyn CadCommand>>,
+    /// `suspended_cmd` was parked by a transparent command (`'ZOOM`) and is
+    /// restored as soon as the transparent one ends.
+    pub(super) transparent_resume: bool,
 }
 
 impl DocumentTab {
@@ -642,6 +645,7 @@ impl DocumentTab {
             zoom_dynamic_mode: false,
             plugin_state: HashMap::new(),
             suspended_cmd: None,
+            transparent_resume: false,
         }
     }