✨ feat(frontend): 升级 DataGrid 组件并引入高性能拖拽交互

- 实现基于原生 DOM 事件的零渲染列宽拖拽，彻底解决卡顿与误触排序问题
- 查询编辑器集成 DataGrid，支持 SQL 结果直接编辑与事务提交
- 侧边栏新增上下文感知的 "新建查询" 快捷入口
- 优化 TabManager 渲染逻辑与全局布局，消除不必要的滚动条

internal/app/app.go

@@ -0,0 +1,72 @@
+package app
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"GoNavi-Wails/internal/connection"
+	"GoNavi-Wails/internal/db"
+)
+
+// App struct
+type App struct {
+	ctx     context.Context
+	dbCache map[string]db.Database // Cache for DB connections
+	mu      sync.Mutex             // Mutex for cache access
+}
+
+// NewApp creates a new App application struct
+func NewApp() *App {
+	return &App{
+		dbCache: make(map[string]db.Database),
+	}
+}
+
+// Startup is called when the app starts. The context is saved
+// so we can call the runtime methods
+func (a *App) Startup(ctx context.Context) {
+	a.ctx = ctx
+}
+
+// Shutdown is called when the app terminates
+func (a *App) Shutdown(ctx context.Context) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	for _, dbInst := range a.dbCache {
+		dbInst.Close()
+	}
+}
+
+// Helper: Generate a unique key for the connection config
+func getCacheKey(config connection.ConnectionConfig) string {
+	return fmt.Sprintf("%s|%s|%s:%d|%s|%s|%v", config.Type, config.User, config.Host, config.Port, config.Database, config.SSH.Host, config.UseSSH)
+}
+
+// Helper: Get or create a database connection
+func (a *App) getDatabase(config connection.ConnectionConfig) (db.Database, error) {
+	key := getCacheKey(config)
+
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if dbInst, ok := a.dbCache[key]; ok {
+		if err := dbInst.Ping(); err == nil {
+			return dbInst, nil
+		}
+		dbInst.Close()
+		delete(a.dbCache, key)
+	}
+
+	dbInst, err := db.NewDatabase(config.Type)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := dbInst.Connect(config); err != nil {
+		return nil, err
+	}
+
+	a.dbCache[key] = dbInst
+	return dbInst, nil
+}