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/base.go

@@ -0,0 +1,40 @@
+package sdk
+
+import (
+	"context"
+	"fmt"
+)
+
+// BasePlugin provides default implementations for optional Plugin methods.
+type BasePlugin struct{}
+
+func (BasePlugin) Init(_ context.Context, _ PluginConfig) error { return nil }
+
+func (BasePlugin) Start(_ context.Context, _ HostAPI) error { return nil }
+
+func (BasePlugin) Stop(_ context.Context) error { return nil }
+
+func (BasePlugin) Health(_ context.Context) error { return nil }
+
+// BaseTool provides a Validate default that checks required parameters.
+type BaseTool struct {
+	Def        ToolDefinition
+	Required   []string
+}
+
+func (b BaseTool) Definition() ToolDefinition { return b.Def }
+
+func (b BaseTool) Complexity() ToolComplexity { return ComplexitySimple }
+
+func (b BaseTool) Validate(args map[string]interface{}) error {
+	for _, key := range b.Required {
+		if _, ok := args[key]; !ok {
+			return fmt.Errorf("missing required parameter: %s", key)
+		}
+	}
+	return nil
+}
+
+func (b BaseTool) Execute(_ context.Context, _ map[string]interface{}) (*ToolResult, error) {
+	return nil, fmt.Errorf("not implemented")
+}