Add ocs_doc_api: object-oriented CAD entity API (v2)

New crate crates/ocs_doc_api: object-centric facade (DocApi -> Document ->
collections -> typed handles), transport-agnostic wire layer (DocApiEnvelope =
single op | read-only query batch), per-op autocommit (no write transactions),
bulk ops with upfront-validation all-or-nothing, structured ApiError, and
build-time codegen (spec/entities.toml -> ops/query enums, api_reference.md,
binding_schema.json).

ocs_plugin_api: append-only PluginRequest::DocApiRequest / PluginResponse::
DocApiResponse (serde_bytes payload) + defaulted HostApi::doc_api_dispatch.

Host: DocApiBackend impl for HostSession (src/app/doc_api.rs) mapping to scene
primitives (solid_models lift-on-miss, register_prepared_solid_model, meshes
metrics), entity conversions (doc_api_convert.rs), HostSession accessors +
doc_api_dispatch override.

Tests: 592 host lib (incl. 7 DocApi integration tests: create/boolean/query,
unknown-id, transform-many all-or-nothing, query-batch cap, 2D/geometric/DWG
roundtrips), 8 crate unit tests. Examples + README/ARCHITECTURE/IMPLEMENTATION docs.

crates/ocs_doc_api/src/query.rs

@@ -0,0 +1,61 @@
+//! Read queries — typed, transport-agnostic reads of entity state (plan §5).
+//! The `Query` enum is GENERATED into `crate::gen` by `build.rs`; this module
+//! re-exports it and holds the hand-written result DTOs.
+
+use serde::{Deserialize, Serialize};
+
+use crate::id::ObjectId;
+use crate::revision::GeometryRevision;
+
+pub use crate::gen::Query;
+
+/// Axis-aligned bounding box (plain-data mirror of the kernel's non-serde `Aabb`).
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub struct Aabb {
+    pub min: [f64; 3],
+    pub max: [f64; 3],
+}
+
+impl Aabb {
+    pub fn overlaps(&self, other: &Aabb) -> bool {
+        (0..3).all(|i| self.min[i] <= other.max[i] && other.min[i] <= self.max[i])
+    }
+}
+
+/// A generic, untyped view of an entity returned by [`Query::GetEntity`].
+/// Family-specific data lives in the typed construction specs; this carries
+/// identity + kind + a coarse bounding box so any first-level entity is readable.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct EntityView {
+    pub id: ObjectId,
+    /// The acadrust `EntityType` variant name (e.g. "Solid3D", "Line").
+    pub kind: String,
+    pub bounds: Option<Aabb>,
+}
+
+/// The result of a single [`Query`] (one per query in a `Queries` batch).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum QueryResult {
+    Entity(EntityView),
+    Bounds(Aabb),
+    Centroid([f64; 3]),
+    Volume(f64),
+    /// Whether two entities' bounds overlap (two-phase conditional modelling).
+    Intersects(bool),
+    Revision(GeometryRevision),
+}
+
+/// Convenience: the query name for diagnostics.
+impl crate::gen::Query {
+    pub fn query_name(&self) -> &'static str {
+        use crate::gen::Query::*;
+        match self {
+            GetEntity { .. } => "GetEntity",
+            GetBounds { .. } => "GetBounds",
+            GetCentroid { .. } => "GetCentroid",
+            GetVolume { .. } => "GetVolume",
+            GetIntersects { .. } => "GetIntersects",
+            GetGeometryRevision => "GetGeometryRevision",
+        }
+    }
+}