refactor: migrate built-in plugins to SDK-only interface

- Six-phase plan complete: webui/cli/healthcheck/pluginmgr/clawhubadapter
  now interact with the kernel exclusively via internal/sdk interfaces;
  all Configure() calls and package-level global injection removed
- buildSDK in internal/plugin/registry.go is the single assembly point
- Add internal/sdk/events.go exporting event types/constants
- Fix ProviderManager cooldown sharing: LuaAdaptedProvider.Name() now
  returns the source name instead of lua_<adapter>, so multiple sources
  sharing an adapter (single script load via shared VM AdapterCache) no
  longer share failure-cooldown state
- Verified: build/vet/tests green, deployed to homeagent.service with
  full plugin capability testing via local OpenAI-compatible mock

internal/sdk/knowledge.go

@@ -2,5 +2,13 @@ package sdk
 
 import pubsdk "gitcode.com/JianFeeeee/homeagent-sdk/sdk"
 
-type KnowledgeAPI = pubsdk.KnowledgeAPI
+// KnowledgeAPI 是内置插件使用的全量知识库接口。
+type KnowledgeAPI interface {
+	pubsdk.KnowledgeAPI
+	// Stats 返回知识库的运行统计。
+	Stats() map[string]interface{}
+	// Remove 按名称删除一条知识。
+	Remove(name string) error
+}
+
 type Knowledge = pubsdk.Knowledge