Add MCP server to AST tool

Integrates the MCP server functionality into the AST tool binary. This
allows the tool to act as a server for LLM integration, enabling
communication over stdio. The server can list available bindings and
execute scripts.

src/ast/environment.rs

@@ -600,6 +600,19 @@ impl Environment {
     }
 
 
+    /// Returns the names of all bindings registered in the fixed RTL scope.
+    /// Useful for introspection (e.g., MCP server listing available built-ins).
+    pub fn list_bindings(&self) -> Vec<String> {
+        let root_scopes = self.root_scopes.borrow();
+        let mut names: Vec<String> = root_scopes[0]
+            .locals
+            .keys()
+            .map(|sym| sym.name.to_string())
+            .collect();
+        names.sort();
+        names
+    }
+
     pub fn dump_ast(&self, source: &str) -> Result<String, String> {
         self.preload_dependencies(source, None)?;
         let compiled = self.compile(source).into_result()?;