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/settings.go

@@ -2,5 +2,13 @@ package sdk
 
 import pubsdk "gitcode.com/JianFeeeee/homeagent-sdk/sdk"
 
-type SettingsAPI = pubsdk.SettingsAPI
+// SettingsAPI 是内置插件使用的全量配置接口。
+type SettingsAPI interface {
+	pubsdk.SettingsAPI
+	// DefsCore 返回核心配置表中匹配前缀的配置定义。
+	DefsCore(prefix string) []*ConfigDef
+	// DefsPlugin 返回另一个插件的配置定义。
+	DefsPlugin(plugin, prefix string) []*ConfigDef
+}
+
 type ConfigDef = pubsdk.ConfigDef