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/tool.go

@@ -0,0 +1,20 @@
+package sdk
+
+// ToolSource 描述内核工具注册表/执行器的只读视图（由 StageHost 实现）。
+// 用接口而非具体类型，避免 sdk 依赖内核包（内核包反向依赖 sdk）。
+type ToolSource interface {
+	GetToolDefs() []ToolDef
+	ToolDef(name string) *ToolDef
+	ExecuteTool(name string, args map[string]interface{}) (interface{}, error)
+}
+
+// ToolAPI exposes the kernel tool registry and executor
+// (StageHost for plugin tools + IOManager for device/channel tools).
+type ToolAPI interface {
+	// GetToolDefs returns all tools registered on the stage host (plugin tools).
+	GetToolDefs() []ToolDef
+	// GetAllTools returns all tools exposed by IO devices/channels.
+	GetAllTools() []ToolDef
+	// ExecuteTool executes a tool by name, resolving across the stage host first.
+	ExecuteTool(name string, args map[string]interface{}) (interface{}, error)
+}