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>

src/entities/field.rs

@@ -1,15 +1,15 @@
 //! Host-side glue for dynamic text field evaluation.
 //!
 //! The field language (DIESEL + AcVar), the field structure/linkage, and all
-//! date math live in the reader library ([`acadrust::fields`]). OCS only
+//! date math live in the reader library ([`codec::fields`]). OCS only
 //! supplies the **environment** — the current clock, OS login and environment
 //! variables — through [`FieldContext`]. A DWG library must stay deterministic
 //! and platform-neutral, so the one genuinely system-specific bit (reading the
 //! clock / OS user) lives here in the app instead.
 
-use acadrust::fields::FieldContext;
-use acadrust::types::Handle;
-use acadrust::CadDocument;
+use codec::fields::FieldContext;
+use codec::types::Handle;
+use codec::CadDocument;
 
 /// OCS's environment provider for field evaluation.
 struct OcsFieldContext;
@@ -50,7 +50,7 @@ impl FieldContext for OcsFieldContext {
 /// Re-evaluate the field hosted by entity `host` (usually an MTEXT), or `None`
 /// to keep the cached text. Thin wrapper over the library engine.
 pub fn resolve(document: &CadDocument, host: Handle) -> Option<String> {
-    acadrust::fields::resolve(document, host, &OcsFieldContext)
+    codec::fields::resolve(document, host, &OcsFieldContext)
 }
 
 pub fn resolve_handle(
@@ -58,7 +58,7 @@ pub fn resolve_handle(
     field: Handle,
     host: Handle,
 ) -> Option<String> {
-    acadrust::fields::resolve_handle(document, field, host, &OcsFieldContext)
+    codec::fields::resolve_handle(document, field, host, &OcsFieldContext)
 }
 
 /// Seconds since the Unix epoch. Native uses the system clock; wasm uses the JS