refactor: rename DTree to DValue

site/doc/pages/unit_call.txt

@@ -1,11 +1,11 @@
 :sig
-DTree* unit_call(String file_name, String function_name, DTree* call_param = null)
+DValue* unit_call(String file_name, String function_name, DValue* call_param = null)
 
 :params
 file_name : UCE file to load and execute
 function_name : name of the function to invoke
 call_param : optional, call parameter
-return value : DTree* returned from function
+return value : DValue* returned from function
 
 :see
 >ob
@@ -20,7 +20,7 @@ Calls an exported function inside another UCE file.
 
 Use `unit_call()` when you need structured data exchange between units rather than rendered HTML output.
 
-The callee must expose an `EXPORT` function whose name matches `function_name`. Arguments are passed through `call_param`, and the return value is a `DTree*` owned by the callee.
+The callee must expose an `EXPORT` function whose name matches `function_name`. Arguments are passed through `call_param`, and the return value is a `DValue*` owned by the callee.
 
 `unit_call()` also understands the request-bound UCE entrypoint names:
 
@@ -31,7 +31,7 @@ The callee must expose an `EXPORT` function whose name matches `function_name`.
 - `ONCE`
 - `INIT`
 
-When `function_name` matches one of those macro-style entrypoints, `unit_call()` does not look for a plain `EXPORT DTree* ...` function. Instead, it translates the name to the generated C++ symbol, uses the current `Request` context, and passes `call_param` into `context.props`, matching the normal component invocation model.
+When `function_name` matches one of those macro-style entrypoints, `unit_call()` does not look for a plain `EXPORT DValue* ...` function. Instead, it translates the name to the generated C++ symbol, uses the current `Request` context, and passes `call_param` into `context.props`, matching the normal component invocation model.
 
 For `RENDER...` and `COMPONENT...`, the unit's `ONCE(Request& context)` hook is still honored automatically before the selected handler runs.
 
@@ -39,7 +39,7 @@ Example:
 
 ```cpp
 // export a function
-EXPORT DTree* test_func(DTree* call_param)
+EXPORT DValue* test_func(DValue* call_param)
 {
 	print("HELLO FROM TEST FUNCTION");
 	return(0);
@@ -52,7 +52,7 @@ unit_call("call_file_funcs.uce", "test_func");
 Calling a named component handler through `unit_call()`:
 
 ```cpp
-DTree props;
+DValue props;
 props["title"] = "Diagnostics";
 props["body"] = "Ready";
 
@@ -62,7 +62,7 @@ unit_call("components/card.uce", "COMPONENT:BODY", &props);
 Calling a page render handler through `unit_call()`:
 
 ```cpp
-DTree props;
+DValue props;
 props["section"] = "summary";
 
 unit_call("reports/summary.uce", "RENDER", &props);