docs: update PG migration status, data models, architecture + add Telegram Mini App flow (v2.8.59)
- Postgres Runtime Cutover Status: 17 migrations (0000–0017), dual-write repo matrix
- Backend Architecture: dual-DB architecture, repo factory, MONGO_CONNECT_MODE modes
- Data Model Overview: 23-model index with PG table names and migration status
- User, PurchaseRequest, SellerOffer, Chat, Dispute: Drizzle schema + cutover status added
- 04 - Flows/Telegram Mini App.md: new doc covering Mini App architecture and flows
- mongo-to-pg-migration-prd.md: status block prepended with 2026-06-03 milestone tracking
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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