Map SectionSymbol, the last unmapped kind

points is canonical; the host derives the point counts and refreshes the
end/tick/label projections with sync_display_fields when it changes, and
validates that style and view-representation references are existing class
objects. The lifecycle test passes every gate in DWG; DXF reopens the symbol
as an unknown entity because cadcodec dispatches SECTIONLINE only inside
blocks (pinned by a canary and already in the cadcodec write-up).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/ocs_plugin_api/build.rs

@@ -793,6 +793,7 @@ fn generate_entity_coverage(out_dir: &Path, registry: &TypeRegistry) {
                     | ("Helix", _)
                     | ("RasterImage", _)
                     | ("Wipeout", _)
+                    | ("SectionSymbol", _)
                     | ("Surface", "u_isolines" | "v_isolines")
                     | ("Ole2Frame", _)
                     | ("Underlay", _)