merge: config + store(UTC DSN) + 自动迁移 [tsk_zRA6fGU1JuHj]

以 main 现有 config 设计为准(FromEnv/*Config/单 DSN/RS256),移植分支新增的 store 层:mysql.go 的 Open(*config.Config) 改用 cfg.DSN、结构化强制 UTC + 会话时区断言;migrate.go + migrations/embed.go 提供 golang-migrate 嵌入式迁移;cmd/migrate/main.go 实现 migrate CLI(读 DB_DSN)。未采用分支的 Load()/PANGOLIN_ 前缀/MySQL 拆分字段(与 main 设计冲突)。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/migrations/embed.go

@@ -0,0 +1,15 @@
+// Package migrations provides the embedded SQL migration files for golang-migrate.
+// Files are named in the golang-migrate convention:
+//
+//	{version}_{title}.up.sql
+//	{version}_{title}.down.sql
+//
+// The FS is consumed by internal/store.MigrateUp / MigrateDown.
+package migrations
+
+import "embed"
+
+// FS contains all *.sql files in this directory, embedded at compile time.
+//
+//go:embed *.sql
+var FS embed.FS