ocs_doc_api: Phase 2b-a (Text/MText annotations)

- CreateText/CreateMText/SetTextContent ops + GetTextContent query (append-only).
- backend add_text/add_mtext/set_text_content/text_content (Text.value/MText.value).
- facade create_text/create_mtext + Text/MText handles with content()/set_content().
- Text/MText coarse bounds + transform (insertion point); ensure_transformable.
- spec Text/MText families; api_reference + binding_schema regenerated; mocks.
- can_modify backend hook (exists + not-locked) for SetTextContent validation.
- consistency baseline extended with the appended variants.
- Test phase2b_text_mtext_create_content_transform -> 605 host lib + 3 consistency green.

crates/ocs_doc_api/src/gen/query_gen.rs

@@ -19,4 +19,6 @@ pub enum Query {
     /// Whether two entities' bounds overlap (two-phase conditional modelling).
     GetIntersects { a: ObjectId, b: ObjectId },
     GetGeometryRevision,
+    /// The text content of a Text/MText annotation.
+    GetTextContent { id: ObjectId },
 }