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

patches/gcp-metadata@8.1.2.patch

@@ -0,0 +1,14 @@
+diff --git a/build/src/index.js b/build/src/index.js
+--- a/build/src/index.js
++++ b/build/src/index.js
+@@ -323,6 +323,10 @@ async function isAvailable() {
+         if (process.env.DEBUG_AUTH) {
+             console.info(err);
+         }
++        // Promise.any() rejects with AggregateError when neither metadata host
++        // is available. This is expected outside GCP, not a warning condition.
++        if (err instanceof AggregateError)
++            return false;
+         if (err.type === 'request-timeout') {
+             // If running in a GCP environment, metadata endpoint should return
+             // within ms.