feat: add Python migration script and successfully test SQLite to PostgreSQL data migration

- Created scripts/migrate-sqlite-to-postgres.py as alternative to TypeScript version
- Handles all type conversions: timestamps, booleans, and JSONB fields
- Successfully migrated all 2,836 rows from SQLite to PostgreSQL
- Verified data integrity: all 6 tables migrated correctly
- Charts: 1, Candles: 2,592, Annotations: 4, Span annotations: 223

src/app/api/span-annotations/export/route.ts

@@ -8,6 +8,9 @@ import { eq, desc } from 'drizzle-orm';
  * 
  * Export span annotations in ML pipeline format (JSON).
  * 
+ * @deprecated The ML service now queries annotations directly from PostgreSQL.
+ * This endpoint is retained for data backup and external analysis purposes only.
+ * 
  * Query params:
  * - chartId: (optional) specific chart ID. If omitted, uses most recent chart.
  * - format: (optional) 'json' (default) or 'csv'