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/hack/plugin-dev/templates/plugin.json.tmpl

@@ -0,0 +1,10 @@
+{
+  "name": "{{.Name}}",
+  "version": "{{.Version}}",
+  "description": "{{.Description}}",
+  "author": "{{.Author}}",
+  "license": "MIT",
+  "entry": "plugin.so",
+  "min_version": "1.0.0",
+  "tags": ["{{.Name}}"]
+}