refactor: create 从 SDD 阶段降级为工具命令，移除阶段配置和提示词

src/core/assembler.ts

@@ -16,15 +16,6 @@ export function assembleDiscussPrompt(config: RuneConfig): string {
   return applyCommandPrefix(discuss.prompt, config);
 }
 
-export function assembleCreatePrompt(config: RuneConfig): string {
-  const create = config.stages.create;
-  if (!create)
-    throw new CommandError("创建阶段未配置", {
-      hint: "请在 .rune/config.yaml 中配置 stages.create",
-    });
-  return applyCommandPrefix(create.prompt, config);
-}
-
 export async function assemblePlanPrompt(
   config: RuneConfig,
   projectRoot: string,