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/ui/icons.rs

@@ -44,6 +44,8 @@ static OSNAP_APPARENT: &[u8] = include_bytes!("../../assets/icons/osnap/apparent
 static OSNAP_PARALLEL: &[u8] = include_bytes!("../../assets/icons/osnap/parallel.svg");
 static OSNAP_GRID: &[u8] = include_bytes!("../../assets/icons/osnap/grid.svg");
 static OSNAP_MTP: &[u8] = include_bytes!("../../assets/icons/osnap/mtp.svg");
+static NAV_PAN: &[u8] = include_bytes!("../../assets/icons/pan.svg");
+static NAV_ZOOM: &[u8] = include_bytes!("../../assets/icons/zoom_in.svg");
 
 static LAY_ON: &[u8] = include_bytes!("../../assets/icons/layers/layon.svg");
 static LAY_OFF: &[u8] = include_bytes!("../../assets/icons/layers/layoff.svg");
@@ -643,6 +645,15 @@ pub fn mtp_icon() -> &'static [u8] {
     OSNAP_MTP
 }
 
+/// Context-menu glyphs for the transparent navigation rows.
+pub fn pan_icon() -> &'static [u8] {
+    NAV_PAN
+}
+
+pub fn zoom_icon() -> &'static [u8] {
+    NAV_ZOOM
+}
+
 /// Layer visibility icon bytes (on / off).
 pub fn layer_visible(visible: bool) -> &'static [u8] {
     if visible {