feat(properties): audit editable vs read-only across all entities

Reclassify every property row to match standard palette behaviour: a row
is editable only when its value maps directly to a stored field AND its
apply_geom_prop handler is wired; computed/derived/count/handle/
cross-object values stay read-only.

Newly editable (all apply-wired): attribute tag/prompt; ellipse major
radius; hatch Double; lwpolyline closed/linetype-gen; mline style;
multileader annotative/landing/background-fill; polyline 2D+3D vertex
coords/segment widths/linetype-gen; shape style; spline control/fit
point coords, weight, fit tolerance, tangents; table break-option flags;
text alignment point, upside-down, backward; underlay display flags.

Corrections: spline Degree -> read-only (editing desynced the knot
vector); removed a duplicate leader "Arrowhead" row.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/entities/leader.rs

@@ -209,7 +209,6 @@ fn properties(leader: &Leader) -> Vec<PropSection> {
             creation_type_str(&leader.creation_type),
             &["With Text", "With Tolerance", "With Block", "No Annotation"],
         ),
-        bool_toggle("Arrowhead", "arrow_enabled", leader.arrow_enabled),
         Property {
             label: "Dim style".into(),
             field: "dimension_style",