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]>

plugins/opencad-python/PLUGIN.md

@@ -181,7 +181,7 @@ positive, and `dimtxsty` must name an existing text style. `Standard` is never
 renamed or deleted; a style that is current or still referenced is never deleted;
 a case-only rename is refused. Style operations act on the active document.
 
-Known persistence limits (cadcodec, see `docs/cadcodec-reader-gaps.md`; the first two are fixed in
+Known persistence limits (opencadcodec, see `docs/cadcodec-reader-gaps.md`; the first two are fixed in
 an open upstream pull request but OCS has not yet adopted it): a DXF
 save drops the backward/upside-down flags of a text style and does not restore a
 dimension style's `dimtxsty` name (the handle link survives); DWG keeps both.
@@ -211,7 +211,7 @@ anonymous or externally referenced blocks, and a case-only rename. Deleting also
 removes the definition's contents. Records list user blocks only (`handle`,
 `name`, `description`, `explodable`, `scale_uniformly`, `base_point`,
 `insert_count`, `entities` as `{handle, kind}`). A DXF save drops the block
-description (cadcodec); DWG keeps it.
+description (opencadcodec); DWG keeps it.
 
 **Block contents.** Add to a definition with `create_entity(kind, block="Part",
 ...)`. It is validated exactly like a model-space entity and the host sets the