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>

crates/ocs_plugin_api/ARCHITECTURE.md

@@ -11,7 +11,7 @@ Internal-facing architecture documentation for `crates/ocs_plugin_api`. For plug
 | Tier | Feature | Dependencies | Purpose |
 |------|---------|--------------|---------|
 | **Core** | default | none | `PluginManifest`, `ApiVersion`, ribbon vocabulary, type registry, version info. Engine crates and external tooling can depend on this cheaply. |
-| **Runtime host surface** | `host` | `acadrust`, `interprocess`, `memmap2`, `rkyv`, etc. | `HostApi`, `BuiltinPlugin`, out-of-process spawn, IPC, shared-memory snapshots, runner. |
+| **Runtime host surface** | `host` | `opencadcodec`, `interprocess`, `memmap2`, `rkyv`, etc. | `HostApi`, `BuiltinPlugin`, out-of-process spawn, IPC, shared-memory snapshots, runner. |
 
 The host and each plugin run in separate OS processes. The host re-executes itself in `--ocs-plugin-runner` mode, the runner dynamically loads the plugin `cdylib`, and the two sides talk over a local socket. Process isolation keeps plugin crashes from affecting the host or other plugins.
 
@@ -38,7 +38,7 @@ The host and each plugin run in separate OS processes. The host re-executes itse
 | [`src/shm.rs`](src/shm.rs) | Shared-memory document snapshot layout, `DocumentSnapshotStore`, `SharedDocumentReader`, V3/V4 view data. |
 | [`src/host_v4.rs`](src/host_v4.rs) | Host-side per-tab V4 snapshot manager. |
 | [`src/type_registry.rs`](src/type_registry.rs) / [`src/type_registry_types.rs`](src/type_registry_types.rs) | Build-time `serde-reflection` registry, embedded JSON, schema types. |
-| [`src/version_info.rs`](src/version_info.rs) | Embedded version metadata and acadrust source-compatibility helper. |
+| [`src/version_info.rs`](src/version_info.rs) | Embedded version metadata and opencadcodec source-compatibility helper. |
 
 ---
 
@@ -48,7 +48,7 @@ The host and each plugin run in separate OS processes. The host re-executes itse
 - `API_VERSION_MIN_SUPPORTED` (currently `2`) is the oldest plugin major the host loads.
 - `OCS_PLUGIN_MAX_API_VERSION` can cap the accepted major at runtime (e.g. `5` to disable V6).
 - A plugin built against major `N` runs on a host whose major is `>= N` because new vtable entries and enum variants are appended at the end.
-- V4 introduces the **acadrust gate**: plugins targeting API v4 or later must resolve the same `acadrust` source as the host (see [`src/version_info.rs`](src/version_info.rs)).
+- V4 introduces the **opencadcodec gate**: plugins targeting API v4 or later must resolve the same `opencadcodec` source as the host (see [`src/version_info.rs`](src/version_info.rs)).
 - V5 introduces `BuiltinPlugin::on_load` and tab-keyed document paths.
 - V6 appends typed system-variable access to `HostApi`; the host currently
   supports `CLAYER` and `SNAPANG` (plus a read-only `CTAB`).
@@ -222,7 +222,7 @@ Broadcasting is V4-gated inside `PluginManager::broadcast_notification`: V2/V3 p
 The crate embeds two JSON blobs at build time:
 
 - **Type registry** (`OUT_DIR/type_registry.json`) — a language-binding-friendly schema for every editor record root and its dependent types, generated by `serde-reflection` in `build.rs`. See [`src/type_registry.rs`](src/type_registry.rs).
-- **Version info** (`OUT_DIR/version_info.json`) — host version, `ocs_plugin_api` version, `acadrust` version and source, `rustc` version, API versions, build timestamp. See [`src/version_info.rs`](src/version_info.rs).
+- **Version info** (`OUT_DIR/version_info.json`) — host version, `ocs_plugin_api` version, `opencadcodec` version and source, `rustc` version, API versions, build timestamp. See [`src/version_info.rs`](src/version_info.rs).
 
 Both are accessible without enabling the `host` feature.