feat: converge dynamic plugins onto canonical homeagent-sdk

- Separate built-in plugin interface from external plugin interface
- Route dynamic plugin loading through homeagent-sdk/sdk using reflection
- Turn internal/sdk into an enhanced wrapper over canonical SDK types
- Vendor SDK repo snapshot under third_party/homeagent-sdk for stable builds
- Keep internal constructors/adapters for memory, knowledge, llm, settings
- Align dynamic QQ loading with canonical SDK chain

third_party/homeagent-sdk/example/files/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "files",
+  "version": "1.0.0",
+  "description": "文件系统操作插件，提供文件读写、编辑、目录列表等工具",
+  "author": "HomeAgent",
+  "entry": "plugin.so",
+  "tags": ["files", "filesystem", "io"]
+}