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/core/test/plugin/fixtures/models-dev.json

@@ -0,0 +1,14 @@
+{
+  "acme": {
+    "id": "acme",
+    "name": "Acme",
+    "env": ["ACME_API_KEY"],
+    "models": {}
+  },
+  "local": {
+    "id": "local",
+    "name": "Local",
+    "env": [],
+    "models": {}
+  }
+}

packages/core/test/plugin/fixtures/provider-factory.ts

@@ -0,0 +1,9 @@
+export function createFixtureProvider(options: Record<string, unknown>) {
+  const captured = Object.fromEntries(Object.entries(options))
+  return Object.assign((modelID: string) => ({ modelID, options: captured }), {
+    options: captured,
+    languageModel(modelID: string) {
+      return { modelID, options: captured }
+    },
+  })
+}