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 <[email protected]>

docs/native-vs-web.md

@@ -28,7 +28,7 @@ crates reach `vtkio → xz2 → lzma-sys` — a C library that cannot cross-comp
 to `wasm32` — so the web build dropped a `solid3d` feature and the Model tab,
 solid tessellation and ACIS import all did nothing there.
 
-The kernel is now cadkernel, which is pure Rust and has no C dependency at
+The kernel is now opencadkernel, which is pure Rust and has no C dependency at
 all, so none of that applies and the feature is gone. The web build makes
 primitives, runs booleans, draws ACIS solids read from a file and writes them
 back out as exact geometry, exactly as the desktop build does.