feat: Phase 3 插件与工具系统 — Plugin SDK + Plugin Manager + 13内置插件 (40文件, 3293行)

- Plugin SDK: Plugin/Tool/ComplexTool/HostAPI 标准化接口
- Plugin Manager: 插件生命周期管理 (Install/Enable/Disable/Uninstall/Reload)
- Tool Registry: 聚合工具注册表 (Register/Execute/Dispatch)
- 13 个内置插件: 将原有硬编码工具迁移为标准插件格式
- REST API: 11 个端点 (net/http, 零外部依赖)
- ai-core 集成: PluginManagerClient 替代本地工具调用
- plugin.json 元数据: 每个插件含完整 author/version/category/permissions

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/plugin-manager/internal/sdk/plugin.go

@@ -0,0 +1,49 @@
+package sdk
+
+import (
+	"context"
+	"net/http"
+)
+
+// Plugin is the main interface every plugin must implement.
+type Plugin interface {
+	Metadata() PluginMetadata
+	Init(ctx context.Context, config PluginConfig) error
+	Start(ctx context.Context, host HostAPI) error
+	Stop(ctx context.Context) error
+	Health(ctx context.Context) error
+	Tools() []Tool
+}
+
+// Tool is the interface every tool must implement.
+type Tool interface {
+	Definition() ToolDefinition
+	Execute(ctx context.Context, args map[string]interface{}) (*ToolResult, error)
+	Validate(args map[string]interface{}) error
+	Complexity() ToolComplexity
+}
+
+// ComplexTool extends Tool for async multi-round execution.
+type ComplexTool interface {
+	Tool
+	ExecuteAsync(ctx context.Context, args map[string]interface{}) (<-chan ToolProgress, error)
+	Cancel(ctx context.Context, executionID string) error
+}
+
+// HostAPI gives plugins access to Cyrene core capabilities.
+type HostAPI interface {
+	CallLLM(ctx context.Context, messages []LLMMessage) (*LLMResponse, error)
+	SearchMemory(ctx context.Context, userID, query string, limit int) ([]MemoryEntry, error)
+	StoreMemory(ctx context.Context, entry MemoryEntry) error
+	Logger() Logger
+	GetConfig(key string) (string, error)
+	SetConfig(key, value string) error
+	PublishEvent(ctx context.Context, event map[string]interface{}) error
+	HTTPClient() *http.Client
+}
+
+// Logger is a minimal logging interface for plugins.
+type Logger interface {
+	Printf(format string, args ...interface{})
+	Println(args ...interface{})
+}