feat: implement PDF annotation extraction and inspector API endpoints via C++ bindings

gateway/app/routers/documents/content.py

@@ -111,6 +111,7 @@ def get_document_annotations(document_id: str) -> list[AnnotationResponse]:
                         content=a.content,
                         timestamp=getattr(a, "timestamp", None),
                         pageIndex=a.page_index,
+                        thickness=getattr(a, "thickness", None),
                         paths=[[{"x": p.x, "y": p.y} for p in stroke] for stroke in getattr(a, "paths", [])],
                         quadPoints=getattr(a, "quad_points", []),
                         fieldName=getattr(a, "field_name", None),

gateway/app/schemas/annotation.py

@@ -13,6 +13,7 @@ class AnnotationResponse(BaseModel):
     content: str
     timestamp: str | None = None
     pageIndex: int
+    thickness: float | None = None
     paths: list[list[dict[str, float]]] = []
     quadPoints: list[list[dict[str, float]]] = []