chore: 移除 environment-runner stub 及其 cli.tsx fast-path

与 self-hosted-runner 相同模式的 sibling（工作流 1 verifier 建议同步处理）：

- 删除 src/environment-runner/main.ts（自动生成的 Promise.resolve() stub）
- 同步移除 src/entrypoints/cli.tsx 中 feature('BYOC_ENVIRONMENT_RUNNER') 守卫的 fast-path 分支
- 清理两个空目录（src/self-hosted-runner/、src/environment-runner/）

BYOC_ENVIRONMENT_RUNNER flag 不在 build.ts DEFAULT_BUILD_FEATURES 也不在 dev 默认列表，所有默认配置下整段为构建期死代码。

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

src/entrypoints/cli.tsx

@@ -314,15 +314,6 @@ async function main(): Promise<void> {
     process.exit(0);
   }
 
-  // Fast-path for `claude environment-runner`: headless BYOC runner.
-  // feature() must stay inline for build-time dead code elimination.
-  if (feature('BYOC_ENVIRONMENT_RUNNER') && args[0] === 'environment-runner') {
-    profileCheckpoint('cli_environment_runner_path');
-    const { environmentRunnerMain } = await import('../environment-runner/main.js');
-    await environmentRunnerMain(args.slice(1));
-    return;
-  }
-
   // Fast-path for --worktree --tmux: exec into tmux before loading full CLI
   const hasTmuxFlag = args.includes('--tmux') || args.includes('--tmux=classic');
   if (

src/environment-runner/main.ts

@@ -1,4 +0,0 @@
-// Auto-generated stub — replace with real implementation
-export {}
-export const environmentRunnerMain: (args: string[]) => Promise<void> = () =>
-  Promise.resolve()