🐛 fix(oceanbase): 修复 OceanBase 协议模式识别与缓存隔离

- 支持 MySQL/Oracle 租户协议在前后端统一解析
- 拒绝 Native 协议并避免误回退为 MySQL
- 修复 Oracle 模式下元数据、DDL、SQL 方言识别
- 修复连接缓存键与实际协议解析优先级不一致问题
- 补充前后端协议解析与缓存隔离回归测试

internal/connection/types.go

@@ -104,7 +104,7 @@ type ConnectionConfig struct {
 	RedisDB              int              `json:"redisDB,omitempty"`              // Redis database index (0-15)
 	URI                  string           `json:"uri,omitempty"`                  // Connection URI for copy/paste
 	ClickHouseProtocol   string           `json:"clickHouseProtocol,omitempty"`   // auto | http | native
-	OceanBaseProtocol    string           `json:"oceanBaseProtocol,omitempty"`    // mysql | oracle
+	OceanBaseProtocol    string           `json:"oceanBaseProtocol,omitempty"`    // OceanBase tenant compatibility protocol: mysql | oracle
 	Hosts                []string         `json:"hosts,omitempty"`                // Multi-host addresses: host:port
 	Topology             string           `json:"topology,omitempty"`             // single | replica | cluster
 	MySQLReplicaUser     string           `json:"mysqlReplicaUser,omitempty"`     // MySQL replica auth user