refactor: rename DTree to DValue

site/doc/pages/0_Request.txt

@@ -24,7 +24,7 @@ ws_message
 ws_connection_id
 ws_connections
 ws_send
-0_DTree
+0_DValue
 StringMap
 UploadedFile
 
@@ -120,7 +120,7 @@ Raw request body. For WebSocket handlers, this is the current message payload.
 Use this for JSON APIs:
 
 ```cpp
-DTree body = json_decode(context.in);
+DValue body = json_decode(context.in);
 ```
 
 ### `context.uploaded_files`
@@ -165,7 +165,7 @@ Related helpers:
 
 ### `context.call`
 
-Type: `DTree`
+Type: `DValue`
 
 General request-local scratch/configuration tree. It is shared by the page, components, and unit calls participating in the current request. Use it for app-level request state, fragments, router results, page type, page title, and other values that need to be read by later components.
 
@@ -181,7 +181,7 @@ Prefer clear top-level names when state is app-wide (`route`, `fragments`) and n
 
 ### `context.cfg`
 
-Type: `DTree`
+Type: `DValue`
 
 Request-local structured configuration. The runtime does not fill this with application config by default; application code may assign it during boot/setup:
 
@@ -199,19 +199,19 @@ String site_name = context.cfg.get_by_path("site/name").to_string();
 
 ### `context.props`
 
-Type: `DTree`
+Type: `DValue`
 
 Invocation-local props for `component()`, `component_render()`, and macro-style `unit_call()` entrypoints. During a component call, the runtime temporarily replaces `context.props` with the props passed to that component and restores the previous value after the call returns.
 
 ```cpp
-DTree props;
+DValue props;
 props["title"] = "Dashboard";
 print(component("components/card", props, context));
 ```
 
 ### `context.connection`
 
-Type: `DTree`
+Type: `DValue`
 
 WebSocket connection-local state. Mutations persist across `WS(Request& context)` calls for the same socket.
 
@@ -394,7 +394,7 @@ RENDER(Request& context)
 RENDER(Request& context)
 {
     context.header["Content-Type"] = "application/json";
-    DTree response;
+    DValue response;
     response["ok"].set_bool(true);
     print(json_encode(response));
 }
@@ -413,7 +413,7 @@ RENDER(Request& context)
 ### Component props
 
 ```cpp
-DTree props;
+DValue props;
 props["title"] = "Welcome";
 print(component("components/card", props, context));
 ```