assistant2: Add tool selector (#26480)

This PR adds a tool selector to Assistant 2 to facilitate customizing
the tools that the model sees:

<img width="1297" alt="Screenshot 2025-03-11 at 4 25 31 PM"
src="https://github.com/user-attachments/assets/7a656343-83bc-4546-9430-6a5f7ff1fd08"
/>

Release Notes:

- N/A

crates/assistant2/src/thread.rs

@@ -355,16 +355,13 @@ impl Thread {
                 input_schema: ScriptingTool::input_schema(),
             });
 
-            tools.extend(
-                self.tools()
-                    .tools(cx)
-                    .into_iter()
-                    .map(|tool| LanguageModelRequestTool {
-                        name: tool.name(),
-                        description: tool.description(),
-                        input_schema: tool.input_schema(),
-                    }),
-            );
+            tools.extend(self.tools().enabled_tools(cx).into_iter().map(|tool| {
+                LanguageModelRequestTool {
+                    name: tool.name(),
+                    description: tool.description(),
+                    input_schema: tool.input_schema(),
+                }
+            }));
 
             request.tools = tools;
         }