Support Color in the Python adapter generator; map Leader.override_color

Color converts as {'kind': ByLayer|None|ByBlock|Index|Rgb, 'value': ...}.
Leader.override_color is now writable; neither DWG nor DXF stores it, which
is recorded as a fourth persistence blocker with a canary assertion.

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

crates/ocs_plugin_api/build.rs

@@ -778,6 +778,7 @@ fn generate_entity_coverage(out_dir: &Path, registry: &TypeRegistry) {
                             | "text_height"
                             | "text_width"
                             | "vertices"
+                            | "override_color"
                             | "annotation_handle"
                             | "normal"
                             | "horizontal_direction"

crates/ocs_plugin_api/entity_coverage_policy.json

@@ -281,6 +281,7 @@
       "text_height",
       "text_width",
       "vertices",
+      "override_color",
       "annotation_handle",
       "normal",
       "horizontal_direction",

crates/ocs_plugin_api/src/entity_coverage.rs

@@ -1684,6 +1684,7 @@ mod tests {
                 "Leader.text_width".to_owned(),
                 "Leader.vertices".to_owned(),
                 "Leader.annotation_handle".to_owned(),
+                "Leader.override_color".to_owned(),
                 "Leader.normal".to_owned(),
                 "Leader.horizontal_direction".to_owned(),
                 "Leader.block_offset".to_owned(),