新增：Markdown编辑器/数据库优化/安全修复

- Markdown 编辑器：实时预览、PDF 导出、独立查看器
- 数据库优化：动态连接池、查询缓存、Redis Pipeline
- 窗口置顶功能
- 文件系统增强：右键菜单、编辑器集成、收藏夹重构
- 安全修复：XSS 防护、路径穿越、HTML 注入
- 代码质量：正则预编译、缓存锁优化、死代码清理

internal/dbclient/pool.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"sync"
+	"time"
 
 	"u-desk/internal/common"
 	"u-desk/internal/crypto"
@@ -18,7 +19,10 @@ type ConnectionPool struct {
 	mongoClients map[uint]*MongoClient
 
 	// 新增：MySQL 真连接池
-	mysqlPool   *MySQLConnectionPool
+	mysqlPool     *MySQLConnectionPool
+	
+	// 查询优化器
+	queryOptimizer *QueryOptimizer
 
 	mu           sync.RWMutex
 }
@@ -38,18 +42,37 @@ func GetPool() *ConnectionPool {
 		// 启动维护协程
 		mysqlPool.StartMaintenance()
 
+		// 创建查询优化器
+		queryOptimizer := NewQueryOptimizer(nil)
+
 		globalPool = &ConnectionPool{
 			mysqlClients: make(map[uint]*MySQLClient),
 			redisClients: make(map[uint]*RedisClient),
 			mongoClients: make(map[uint]*MongoClient),
-			mysqlPool:    mysqlPool,
+			mysqlPool:     mysqlPool,
+			queryOptimizer: queryOptimizer,
 		}
 	})
 	return globalPool
 }
 
+// PooledClient 带释放语义的客户端包装
+type PooledClient struct {
+	Client  *MySQLClient
+	entry   *MySQLPoolEntry
+	pool    *MySQLConnectionPool
+	fromPool bool
+}
+
+// Release 释放连接回连接池
+func (pc *PooledClient) Release() {
+	if pc.fromPool && pc.pool != nil && pc.entry != nil {
+		pc.pool.Release(pc.entry)
+	}
+}
+
 // GetMySQLClient 获取或创建 MySQL 客户端（使用连接池）
-func (p *ConnectionPool) GetMySQLClient(conn *models.DbConnection) (*MySQLClient, error) {
+func (p *ConnectionPool) GetMySQLClient(conn *models.DbConnection) *PooledClient {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
@@ -57,16 +80,25 @@ func (p *ConnectionPool) GetMySQLClient(conn *models.DbConnection) (*MySQLClient
 	if p.mysqlPool != nil {
 		entry, err := p.mysqlPool.Acquire(conn)
 		if err == nil {
-			// 成功从池中获取连接
-			return entry.Client, nil
+			return &PooledClient{Client: entry.Client, entry: entry, pool: p.mysqlPool, fromPool: true}
 		}
-
-		// 连接池错误，返回
-		return nil, err
+		p.logPoolError("Acquire failed", err)
 	}
 
-	// 降级到原有逻辑（如果连接池未初始化）
-	return p.getMySQLClientLegacy(conn)
+	// 降级到原有逻辑
+	client, err := p.getMySQLClientLegacy(conn)
+	if err != nil {
+		return &PooledClient{Client: nil, fromPool: false}
+	}
+	return &PooledClient{Client: client, fromPool: false}
+}
+
+// logPoolError 记录连接池错误
+func (p *ConnectionPool) logPoolError(operation string, err error) {
+	if p.queryOptimizer != nil {
+		// 通过查询优化器记录错误
+		p.queryOptimizer.RecordPoolError(operation, err)
+	}
 }
 
 // getMySQLClientLegacy 原有的 MySQL 客户端获取逻辑（向后兼容）
@@ -115,6 +147,92 @@ func (p *ConnectionPool) GetMySQLPoolStats() *PoolStats {
 	return nil
 }
 
+// OptimizeQuery 优化查询执行
+func (p *ConnectionPool) OptimizeQuery(ctx context.Context, conn *models.DbConnection, sqlStr string, database string) (*QueryResult, time.Duration, error) {
+	pc := p.GetMySQLClient(conn)
+	if pc.Client == nil {
+		return nil, 0, fmt.Errorf("获取 MySQL 连接失败")
+	}
+	defer pc.Release()
+
+	// 使用查询优化器
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.OptimizeQuery(ctx, pc.Client, sqlStr, database)
+	}
+
+	// 降级到普通查询
+	startTime := time.Now()
+	result, err := pc.Client.ExecuteQuery(ctx, sqlStr, database)
+	duration := time.Since(startTime)
+	return result, duration, err
+}
+
+// ExecuteOptimizedUpdate 执行优化的更新操作
+func (p *ConnectionPool) ExecuteOptimizedUpdate(ctx context.Context, conn *models.DbConnection, sqlStr string, database string) (int64, time.Duration, error) {
+	pc := p.GetMySQLClient(conn)
+	if pc.Client == nil {
+		return 0, 0, fmt.Errorf("获取 MySQL 连接失败")
+	}
+	defer pc.Release()
+
+	// 使用查询优化器
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.ExecuteOptimizedUpdate(ctx, pc.Client, sqlStr, database)
+	}
+
+	// 降级到普通更新
+	startTime := time.Now()
+	result, err := pc.Client.ExecuteUpdate(ctx, sqlStr, database)
+	duration := time.Since(startTime)
+	return result, duration, err
+}
+
+// GetQueryStats 获取查询统计信息
+func (p *ConnectionPool) GetQueryStats() QueryStats {
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.GetQueryStats()
+	}
+	return QueryStats{}
+}
+
+// GetSlowQueries 获取慢查询记录
+func (p *ConnectionPool) GetSlowQueries(limit int) []SlowQuery {
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.GetSlowQueries(limit)
+	}
+	return []SlowQuery{}
+}
+
+// GetIndexSuggestions 获取索引建议
+func (p *ConnectionPool) GetIndexSuggestions(table string) []IndexSuggestion {
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.GetIndexSuggestions(table)
+	}
+	return []IndexSuggestion{}
+}
+
+// GenerateIndexSuggestions 为表生成索引建议
+func (p *ConnectionPool) GenerateIndexSuggestions(ctx context.Context, conn *models.DbConnection, database, table string) error {
+	pc := p.GetMySQLClient(conn)
+	if pc.Client == nil {
+		return fmt.Errorf("获取 MySQL 连接失败")
+	}
+	defer pc.Release()
+
+	// 使用查询优化器
+	if p.queryOptimizer != nil {
+		return p.queryOptimizer.GenerateIndexSuggestions(ctx, pc.Client, database, table)
+	}
+	return nil
+}
+
+// ClearQueryCache 清空查询缓存
+func (p *ConnectionPool) ClearQueryCache() {
+	if p.queryOptimizer != nil {
+		p.queryOptimizer.ClearCache()
+	}
+}
+
 // GetRedisClient 获取或创建 Redis 客户端
 func (p *ConnectionPool) GetRedisClient(conn *models.DbConnection) (*RedisClient, error) {
 	p.mu.Lock()