feat: gh-ost 完整策略引擎 — 13项配置+环境差异+云数据库适配+DDL智能分析

配置项(13项):
- ghost_enabled: 全局开关(默认关闭)
- ghost_default_mode: 默认执行模式(dry_run/execute)
- ghost_osc_priority: OSC优先级(native_first/ghost_first/ghost_only)
- ghost_env_mode: 环境模式(development/production)
- ghost_cloud_type: 云数据库类型(self_hosted/aliyun_rds/polardb/aws_aurora)
- ghost_auto_trigger_rows: 自动触发行数阈值(万)
- ghost_auto_trigger_ddl: 自动触发DDL类型
- ghost_path/chunk_size/max_load/critical_load/max_lag_millis/allow_on_master

新增API:
- GET /ghost/config: 查看全部gh-ost配置
- POST /ghost/analyze: DDL智能分析(解析DDL类型+行数检查+策略推荐)
- 云数据库: --aliyun-rds / --aws 自动适配

策略逻辑:
- native_first + development → 推荐Native DDL
- native_first + production + DDL匹配 → 推荐gh-ost
- ghost_first/ghost_only → 强制gh-ost
- 行数超阈值 → 额外推荐gh-ost

backend/internal/ghost/ghost.go

@@ -28,6 +28,8 @@ type GhOstTask struct {
 	Execute        bool   `json:"execute"`
 	ExactRowCount  bool   `json:"exact_row_count"`
 	PostponeCutOver bool  `json:"postpone_cut_over"`
+	AliyunRDS      bool   `json:"aliyun_rds,omitempty"`  // --aliyun-rds
+	AWSAurora      bool   `json:"aws_aurora,omitempty"`  // --aws
 }
 
 // GhOstResult holds the execution result
@@ -96,6 +98,13 @@ func RunGhOst(ctx context.Context, task GhOstTask, ghOstPath string) (*GhOstResu
 	if task.PostponeCutOver {
 		args = append(args, "--postpone-cut-over-flag-file=/tmp/gh-ost-cutover.flag")
 	}
+	// Cloud-specific flags
+	if task.AliyunRDS {
+		args = append(args, "--aliyun-rds")
+	}
+	if task.AWSAurora {
+		args = append(args, "--aws")
+	}
 
 	// Dry-Run vs Execute
 	// gh-ost defaults to noop (dry-run), only --execute actually applies changes
@@ -235,6 +244,13 @@ func buildArgs(task GhOstTask, ghOstPath string) []string {
 	if task.PostponeCutOver {
 		args = append(args, "--postpone-cut-over-flag-file=/tmp/gh-ost-cutover.flag")
 	}
+	// Cloud-specific flags
+	if task.AliyunRDS {
+		args = append(args, "--aliyun-rds")
+	}
+	if task.AWSAurora {
+		args = append(args, "--aws")
+	}
 
 	// gh-ost defaults to noop, only --execute actually applies changes
 	if task.Execute {