feat: node graph overlay; move to opencadcodec/opencadkernel/opencadgraph

The codec and kernel repositories and crates are renamed opencadcodec and
opencadkernel. Inside OCS they are depended on under short keys, so code
reads `codec::`, `kernel::` and the new `graph::` (opencadgraph, the node
graph engine). File-format and protocol spellings stay as they were: the
ACIS product id `acadrust`, the ACADRUST_* switches and the plugin
version keys `acadrust_version` / `acadrust_source`.

A button left of MCP on the command line opens a translucent node graph
over the viewport, with a palette of object, input, math, logic, list,
text and geometry nodes added by click or drag. An object node owns
drawing entities and its rows are the Properties panel's own rows for
them: the single-object page is extracted from refresh_properties as
entity_property_sections, values use the control protocol's
property_json, and writes go through set_property_value with a property
target override, so the panel, MCP and the graph share one read/write
path. A list reaching an object row makes one entity per element. Each
graph action is one undo step; the canvas pans and zooms.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/opencad-python/entity_manifest.json

@@ -142,7 +142,7 @@
         },
         "smooth_type": {
           "exclude": true,
-          "_comment": "acadrust defines two distinct SmoothSurfaceType enums with the same name (polyline.rs, used by Polyline2D's smooth_surface \u2014 and a separate one private to polyline3d.rs, used here); the type registry's tracer keys purely by name and collapses them, so the generically generated conversion resolves to the wrong one. Needs a hand-written override with the fully qualified acadrust::entities::polyline3d::SmoothSurfaceType path to support, not just a rename."
+          "_comment": "opencadcodec defines two distinct SmoothSurfaceType enums with the same name (polyline.rs, used by Polyline2D's smooth_surface \u2014 and a separate one private to polyline3d.rs, used here); the type registry's tracer keys purely by name and collapses them, so the generically generated conversion resolves to the wrong one. Needs a hand-written override with the fully qualified opencadcodec::entities::polyline3d::SmoothSurfaceType path to support, not just a rename."
         }
       }
     },
@@ -209,7 +209,7 @@
       }
     },
     "Solid": {
-      "rust_constructor": "acadrust::entities::Solid::new(acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO)",
+      "rust_constructor": "codec::entities::Solid::new(codec::types::Vector3::ZERO, codec::types::Vector3::ZERO, codec::types::Vector3::ZERO, codec::types::Vector3::ZERO)",
       "fields": {
         "first_corner": {
           "required": true
@@ -226,7 +226,7 @@
       }
     },
     "Face3D": {
-      "rust_constructor": "acadrust::entities::Face3D::new(acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO, acadrust::types::Vector3::ZERO)",
+      "rust_constructor": "codec::entities::Face3D::new(codec::types::Vector3::ZERO, codec::types::Vector3::ZERO, codec::types::Vector3::ZERO, codec::types::Vector3::ZERO)",
       "fields": {
         "first_corner": {
           "required": true
@@ -275,7 +275,7 @@
           "required": true
         }
       },
-      "rust_constructor": "acadrust::entities::Insert::new(String::new(), acadrust::types::Vector3::ZERO)"
+      "rust_constructor": "codec::entities::Insert::new(String::new(), codec::types::Vector3::ZERO)"
     },
     "Tolerance": {
       "fields": {
@@ -391,7 +391,7 @@
         },
         "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()))?; }"
+          "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(codec::entities::MLineFlags::from_bits).ok_or_else(|| vm.new_value_error(\"MLine.flags has unknown bits\".to_owned()))?; }"
         },
         "start_point": {
           "read_only": true
@@ -559,7 +559,7 @@
       }
     },
     "PolygonMesh": {
-      "rust_constructor": "acadrust::entities::PolygonMeshEntity::default()",
+      "rust_constructor": "codec::entities::PolygonMeshEntity::default()",
       "fields": {
         "vertices": {
           "required": true
@@ -951,7 +951,7 @@
         },
         "raw_flags_90": {
           "read_only": true,
-          "_comment": "Semantics unknown in cadcodec; preserved as read, 0 for a new symbol."
+          "_comment": "Semantics unknown in opencadcodec; preserved as read, 0 for a new symbol."
         },
         "raw_point_record_count": {
           "read_only": true