Complete MLine host model coverage

Maps vertices, flags, justification, normal, scale and style with host
validation and MLineStyle binding. The host recomputes vertex direction,
miter and element parameters on scripted create/edit, so scripts only supply
positions. staged_python_mline_lifecycle_over_real_ipc passes the full gate
including DWG and DXF reopen.

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

plugins/opencad-python/entity_manifest.json

@@ -22,7 +22,8 @@
     "AttributeDefinition",
     "AttributeEntity",
     "Hatch",
-    "Leader"
+    "Leader",
+    "MLine"
   ],
   "base_fields": ["handle", "layer", "owner_handle"],
   "overrides": {
@@ -230,6 +231,22 @@
         "mpolygon_boundary_handle_count": { "exclude": true }
       }
     },
+    "MLine": {
+      "fields": {
+        "vertices": { "required": true },
+        "flags": {
+          "rust_getter": "(VAR.flags.bits() as i64)",
+          "rust_setter": "if let Some(v) = dict.get_item_opt(\"flags\", vm)? { let bits = v.try_into_value::<i64>(vm)?; VAR.flags = i16::try_from(bits).ok().and_then(acadrust::entities::MLineFlags::from_bits).ok_or_else(|| vm.new_value_error(\"MLine.flags has unknown bits\".to_owned()))?; }"
+        },
+        "start_point": { "read_only": true },
+        "style_handle": { "read_only": true },
+        "style_element_count": { "read_only": true },
+        "style_name": {
+          "rust_getter": "VAR.style_name.clone()",
+          "rust_setter": "if let Some(v) = dict.get_item_opt(\"style_name\", vm)? { VAR.style_name = v.try_into_value::<String>(vm)?; VAR.style_handle = None; }"
+        }
+      }
+    },
     "Leader": {
       "fields": {
         "vertices": { "required": true },