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/snap.rs

@@ -416,6 +416,17 @@ impl Snapper {
         self.snap_enabled = true;
     }
 
+    /// One-shot "None" override (Snap Overrides ▸ None): the next pick takes
+    /// the raw cursor point, ignoring every running object snap, after which
+    /// `clear_override` restores the saved configuration.
+    pub fn set_override_none(&mut self) {
+        if self.override_saved.is_none() {
+            self.override_saved = Some((self.enabled.clone(), self.snap_enabled));
+        }
+        self.enabled.clear();
+        self.snap_enabled = false;
+    }
+
     /// Restore the pre-override snap configuration. No-op when inactive.
     pub fn clear_override(&mut self) {
         if let Some((enabled, on)) = self.override_saved.take() {