refactor(migrator): use goose SQL only and auto-import zones on upgrade

移除 Go goose 迁移（bridge/legacy data/zone import），改为 goose SQL 占位
与结构迁移脚本；启动时 Migrate 在删旧列前自动导入历史域名，去掉
migrate-zones 手动命令及文档中的人工导入步骤。

internal/db/migrator/goose/sqlite/202606050001_bridge_legacy.sql

@@ -0,0 +1,7 @@
+-- +goose Up
+-- Historical Wavelet→OpenFlare table rename bridge (formerly Go migration).
+-- Fresh installs and current of_* schemas need no action.
+SELECT 1;
+
+-- +goose Down
+SELECT 1;