refactor: rename DTree to DValue

site/doc/pages/to_stringmap.txt

@@ -1,19 +1,19 @@
 :sig
-StringMap DTree::to_stringmap() const
+StringMap DValue::to_stringmap() const
 
 :params
 return value : a flat `StringMap` projection of the node
 
 :see
 >types
-0_DTree
+0_DValue
 StringMap
 to_string
-dtree_keys
-dtree_values
+dv_keys
+dv_values
 
 :content
-Converts a `DTree` into a flat `StringMap`. This is a read accessor: it is `const`, never creates or modifies nodes, and dereferences internal references automatically.
+Converts a `DValue` into a flat `StringMap`. This is a read accessor: it is `const`, never creates or modifies nodes, and dereferences internal references automatically.
 
 - Map-shaped nodes produce one entry per child, with each child read via `to_string()`. Nested maps flatten to empty strings — this is a one-level projection, not a serializer.
 - A non-empty scalar produces a single `"value"` entry holding the scalar.
@@ -25,7 +25,7 @@ Use this when handing request- or config-shaped data to APIs that take `StringMa
 
 ```cpp
 StringMap params = context.props["filters"].to_stringmap();
-DTree rows = sqlite_query(db, "select * from notes where author = :author", params);
+DValue rows = sqlite_query(db, "select * from notes where author = :author", params);
 ```
 
 For a faithful representation of nested data, use `json_encode()` instead.