fix(migrations): correct migration version from v4.0-to-v4.1 to v4.1-to-v4.2

The migration was incorrectly named as v4.0→v4.1 but was actually performing
the v4.1→v4.2 migration (moving thresholds from UPS-level to action-level).
This meant users upgrading from v4.1 would not get their configs migrated.

Changes:
- Renamed migration file from migration-v4.0-to-v4.1.ts to migration-v4.1-to-v4.2.ts
- Updated class name from MigrationV4_0ToV4_1 to MigrationV4_1ToV4_2
- Updated fromVersion from '4.0' to '4.1'
- Updated toVersion from '4.1' to '4.2'
- Updated shouldRun() to check for config.version === '4.1'
- Updated all imports and exports to reference the new class name
- Updated comments and log messages to reflect v4.1→v4.2 migration

ts/migrations/index.ts

@@ -8,4 +8,4 @@ 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';
-export { MigrationV4_0ToV4_1 } from './migration-v4.0-to-v4.1.ts';
+export { MigrationV4_1ToV4_2 } from './migration-v4.1-to-v4.2.ts';