refactor: remove standalone migrate command, auto-migrate on startup

Migrations already run idempotently during RunServer startup via goose
(which tracks applied versions in goose_db_version). The separate
 command is redundant — removed it and consolidated
serveCmd/configFile/init into server.go.

docs/backend-dev-plan.md

@@ -62,8 +62,7 @@ sub-store/
 ├── main.go                         # 入口，调用 cmd
 ├── cmd/
 │   ├── root.go                     # cobra root command
-│   ├── serve.go                    # sub-store serve (启动 HTTP 服务)
-│   ├── migrate.go                  # sub-store migrate (执行数据库迁移)
+│   ├── serve.go                    # sub-store serve (启动 HTTP 服务，启动时自动 migrate)
 │   └── version.go                  # sub-store version
 ├── internal/
 │   ├── config/
@@ -322,11 +321,11 @@ ON source_cache(cached_at + ttl);
 | 任务 | 产出 | 依赖库 |
 |------|------|--------|
 | go mod init + 依赖引入 | `go.mod` | 全部 |
-| cobra root/serve/migrate/version 命令 | `cmd/*.go` | cobra |
+| cobra root/serve/version 命令 | `cmd/*.go` | cobra |
 | viper 配置加载 | `internal/config/config.go` | viper |
 | logrus 日志初始化 | 日志格式化、级别、输出 | logrus |
 | SQLite 连接初始化 | `internal/database/db.go` | modernc/sqlite, sqlx |
-| goose 迁移执行 | `cmd/migrate.go` | goose |
+| goose 迁移执行（启动时自动） | `internal/database/migrations.go` | goose |
 | 3 个 migration SQL 文件 | `internal/database/migrations/` | |
 | Fiber app 骨架 | 路由注册、健康检查 | fiber/v3 |
 | 优雅关闭 | signal handling | |
@@ -830,11 +829,8 @@ output: YAML with proxies: [{name:"test", type:"ss", ...}]
 # 构建
 go build -o sub-store ./main.go
 
-# 运行
+# 运行（启动时自动执行迁移，幂等）
 ./sub-store serve --config config.yaml
-
-# 迁移
-./sub-store migrate --config config.yaml
 ```
 
 ### 9.2 配置

docs/review-resolutions.md

@@ -42,7 +42,7 @@
 | 30 | importStorage 导入顺序 | settings→sources→templates→collections | `handler/storage.go` |
 | 31 | exportStorage 排除内置模板 | 过滤 BuiltinTemplateIDs | `handler/storage.go` |
 | 32 | source_cache TTL 清理 | 后台 goroutine 定时清理 | `database/cache_repo.go` |
-| 33 | goose 迁移嵌入 | //go:embed + SetBaseFS | `cmd/migrate.go` |
+| 33 | goose 迁移嵌入 | //go:embed + SetBaseFS | `database/migrations.go` |
 | 34 | goroutine 关闭安全 | sync.WaitGroup + context | `service/subscription.go` |
 | 35 | 缓存操作错误吞咽 | recover + 日志，不传播 | `database/cache_repo.go` |
 | 36 | 并发 wait 延迟 | 保留 waitMs 参数 | `service/concurrency.go` |
@@ -491,7 +491,7 @@ func RunMigrations(db *sqlx.DB) error {
 }
 ```
 
-**落地**：`cmd/migrate.go` + `database/migrations/*.sql`。
+**落地**：`database/migrations.go` + `database/migrations/*.sql`。启动时自动执行，幂等（goose 跟踪 `goose_db_version`）。
 
 ---