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/migration-runner.ts

@@ -1,7 +1,7 @@
 import { BaseMigration } from './base-migration.ts';
 import { MigrationV1ToV2 } from './migration-v1-to-v2.ts';
 import { MigrationV3ToV4 } from './migration-v3-to-v4.ts';
-import { MigrationV4_0ToV4_1 } from './migration-v4.0-to-v4.1.ts';
+import { MigrationV4_1ToV4_2 } from './migration-v4.1-to-v4.2.ts';
 import { logger } from '../logger.ts';
 
 /**
@@ -18,8 +18,8 @@ export class MigrationRunner {
     this.migrations = [
       new MigrationV1ToV2(),
       new MigrationV3ToV4(),
-      new MigrationV4_0ToV4_1(),
-      // Add future migrations here (v4.2, v4.3, etc.)
+      new MigrationV4_1ToV4_2(),
+      // Add future migrations here (v4.3, v4.4, etc.)
     ];
 
     // Sort by version order to ensure they run in sequence