fix: re-add DEFAULT_TEXT_MODEL import dropped by merge

Local main's unpushed commits had removed DEFAULT_TEXT_MODEL from the
crate::config import in main.rs, but the merged branch's new code at
two call sites still uses it. Textual three-way merge took the local
import line and the branch's call sites, producing a build break.
Re-add the symbol to the import.

crates/tui/src/main.rs

@@ -51,7 +51,7 @@ mod ui;
 mod utils;
 mod working_set;
 
-use crate::config::{Config, MAX_SUBAGENTS};
+use crate::config::{Config, DEFAULT_TEXT_MODEL, MAX_SUBAGENTS};
 use crate::eval::{EvalHarness, EvalHarnessConfig, ScenarioStepKind};
 use crate::features::Feature;
 use crate::llm_client::LlmClient;