清理未使用的策划会话入口

删除硬编码 quality 模型的 ensure_design_session

保留现有 selected_model_id 创建链路

apps/ai-game-creator-shell/src-tauri/src/agent/runtime_protocol/design_session.rs

@@ -211,21 +211,6 @@ pub(crate) fn write_design_session(root: &Path, session: &DesignSession) -> Resu
     )
 }
 
-pub(crate) fn ensure_design_session(
-    root: &Path,
-    project_id: &str,
-) -> Result<DesignSession, String> {
-    if let Some(session) = read_design_session(root)? {
-        if session.project_id != project_id {
-            return Err("策划会话与当前项目不匹配".to_string());
-        }
-        return Ok(session);
-    }
-    let session = new_design_session(project_id.to_string(), "quality");
-    write_design_session(root, &session)?;
-    Ok(session)
-}
-
 pub(crate) fn design_phase_index(phase: &str) -> Result<usize, String> {
     DESIGN_PHASES
         .iter()