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/mod.rs

@@ -2033,6 +2033,8 @@ pub enum Message {
     /// Mid Between 2 Points from the snap menu: modal 2-pick modifier over
     /// the active point prompt.
     SnapOverrideMtp,
+    /// Snap Overrides ▸ None: the next pick ignores object snaps.
+    SnapOverrideNone,
     /// Close the one-shot snap override menu without picking.
     SnapOverrideClose,
     /// Open a path from the Start tab's recent-documents list (skips the