refactor(beaver): 移除Hermes相关引用和迁移代码，完善Beaver后端主线实现

移除了所有Hermes相关的命名引用，包括：
- 从.gitignore中清理相关构建缓存文件
- 将README中的beaver-home路径配置更新
- 完善backend/README.md文档说明Beaver后端主线实现
- 移除Hermes风格的相关注释和兼容性代码
- 清理nanobot环境变量兼容性处理
- 删除技能迁移和服务迁移相关功能代码
- 更新测试用例中相关命名和函数名

BREAKING CHANGE: 移除了Hermes迁移相关API和CLI命令，不再支持nanobot环境变量兼容性

app-instance/backend/beaver/foundation/config/loader.py

@@ -35,14 +35,12 @@ def default_config_path(*, workspace: str | Path | None = None) -> Path:
 
     Priority:
     1. `BEAVER_CONFIG_PATH`
-    2. `NANOBOT_CONFIG_PATH` for compatibility during migration
-    3. `BEAVER_HOME/config.json`
-    4. `NANOBOT_HOME/config.json` for migration compatibility
-    5. `<workspace>/.beaver/config.json`
-    6. `./.beaver/config.json`
+    2. `BEAVER_HOME/config.json`
+    3. `<workspace>/.beaver/config.json`
+    4. `./.beaver/config.json`
     """
 
-    explicit = os.getenv("BEAVER_CONFIG_PATH") or os.getenv("NANOBOT_CONFIG_PATH")
+    explicit = os.getenv("BEAVER_CONFIG_PATH")
     if explicit:
         return Path(explicit).expanduser()
 
@@ -50,10 +48,6 @@ def default_config_path(*, workspace: str | Path | None = None) -> Path:
     if beaver_home:
         return Path(beaver_home).expanduser() / "config.json"
 
-    nanobot_home = os.getenv("NANOBOT_HOME")
-    if nanobot_home:
-        return Path(nanobot_home).expanduser() / "config.json"
-
     root = Path(workspace).expanduser() if workspace is not None else Path.cwd()
     return root / ".beaver" / "config.json"