feat: 品牌替换 + 启动优化 + AGENTS.md 模板定制

- 品牌替换：OpenCode/opencode → AirCoding/aircoding（16+ 文件）
- Logo ASCII art：修复 left/right 行数不匹配导致的启动崩溃
- 启动诊断：添加 OPENCODE_PRINT_TIMING 计时探针
- dev 模式默认 --pure 跳过外部插件加载
- AGENTS.md 模板：追加 AirCoding 多 Agent 专项段落
- architect prompt + plugin：强化 AGENTS.md 产出验证

packages/tui/test/fixture/fixture.ts

@@ -0,0 +1,13 @@
+import { mkdtemp, realpath, rm } from "node:fs/promises"
+import path from "node:path"
+import os from "node:os"
+
+export async function tmpdir() {
+  const directory = await realpath(await mkdtemp(path.join(os.tmpdir(), "opencode-tui-test-")))
+  return {
+    path: directory,
+    async [Symbol.asyncDispose]() {
+      await rm(directory, { recursive: true, force: true })
+    },
+  }
+}