Remove machine mode entirely from g3

- Delete machine_ui_writer.rs
- Remove --machine CLI flag from cli_args.rs
- Remove run_machine_mode(), run_interactive_machine(), run_autonomous_machine() functions
- Remove handle_machine_command() function
- Simplify OutputMode enum to just use SimpleOutput directly
- Simplify SimpleOutput struct (remove machine_mode field)
- Remove machine_mode parameter from setup_workspace_directory()
- Remove test_machine_option_accepted test
- Disable ACD by default in agent_mode (requires --acd flag)
- Change 'memory checkpoint' message formatting
- Remove dehydration status message

crates/g3-cli/tests/cli_integration_test.rs

@@ -275,20 +275,3 @@ fn test_quiet_option_accepted() {
         "--quiet option should be recognized"
     );
 }
-
-// =============================================================================
-// Test: Machine mode option is accepted
-// =============================================================================
-
-#[test]
-fn test_machine_option_accepted() {
-    let output = Command::new(get_g3_binary())
-        .args(["--machine", "--help"])
-        .output()
-        .expect("Failed to execute g3 with machine option");
-
-    assert!(
-        output.status.success(),
-        "--machine option should be recognized"
-    );
-}