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/config/config.go

@@ -0,0 +1,32 @@
+package config
+
+import "os"
+
+type Config struct {
+	Port       string
+	Env        string
+	DataDir    string
+	IoTSvcURL  string
+}
+
+func Load() *Config {
+	cfg := &Config{
+		Port:      "8094",
+		Env:       "development",
+		DataDir:   "./data",
+		IoTSvcURL: "http://localhost:8093",
+	}
+	if v := os.Getenv("PORT"); v != "" {
+		cfg.Port = v
+	}
+	if v := os.Getenv("ENV"); v != "" {
+		cfg.Env = v
+	}
+	if v := os.Getenv("DATA_DIR"); v != "" {
+		cfg.DataDir = v
+	}
+	if v := os.Getenv("IOT_SERVICE_URL"); v != "" {
+		cfg.IoTSvcURL = v
+	}
+	return cfg
+}