fix: 修复 manifest.json 依赖错误

问题：bleak-mesh 包不存在导致 500 错误
解决：
- 移除不存在的 bleak-mesh 依赖
- 使用 pyserial-asyncio-fast 替代 pyserial-asyncio（HA 推荐）

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

custom_components/sigmesh_gateway/manifest.json

@@ -6,7 +6,7 @@
   "issue_tracker": "https://github.com/impress-sig-mesh/sigmesh_gateway/issues",
   "dependencies": [],
   "codeowners": ["@impress-sig-mesh"],
-  "requirements": ["pyserial-asyncio==0.6", "bleak-mesh>=0.2.0"],
+  "requirements": ["pyserial-asyncio-fast>=0.6"],
   "config_flow": true,
   "iot_class": "local_push",
   "loggers": ["sigmesh_gateway"]