feat(03-01): add shared postgres pool and plugin migrations

Open one pgx stdlib *sql.DB, hand it to GORM, and run per-plugin
gormigrate sets with isolated history tables after an ICU pl-PL check.

Co-authored-by: Cursor <cursoragent@cursor.com>

cmd/summer/main.go

@@ -32,6 +32,9 @@ func toolCommands() []bonfire.Command {
 		parityProxyCommand(),
 		parityRecordCommand(),
 		parityReplayCommand(),
+		delegateCommand("migrate", "Run plugin migrations in the app binary"),
+		delegateRollbackCommand(),
+		delegateCommand("migrate:status", "Show per-plugin migration history in the app binary"),
 	}
 }