feat(migrations): add migration system for v3→v4 config format

- Create abstract BaseMigration class with order, shouldRun(), migrate()
- Add MigrationRunner to execute migrations in order
- Add Migration v1→v2 (snmp → upsDevices)
- Add Migration v3→v4 (upsList → upsDevices)
- Update INupstConfig with version field
- Update loadConfig() to run migrations automatically
- Update saveConfig() to ensure version field and remove legacy fields
- Update Docker test scripts to use real UPS data from .nogit/env.json
- Remove colors.bright (not available in @std/fmt/colors)

Config migrations allow users to jump versions (e.g., v1→v4) with all
intermediate migrations running automatically. Version field tracks
config format for future migrations.

ts/migrations/index.ts

@@ -0,0 +1,10 @@
+/**
+ * Configuration migrations module
+ *
+ * Exports the migration system for upgrading configs between versions.
+ */
+
+export { BaseMigration } from './base-migration.ts';
+export { MigrationRunner } from './migration-runner.ts';
+export { MigrationV1ToV2 } from './migration-v1-to-v2.ts';
+export { MigrationV3ToV4 } from './migration-v3-to-v4.ts';