🐛 Docs & Platform Configuration

Added

• Prisma-first direction: Documentation updated to make Prisma the primary database adapter. Supabase SDK-specific instructions were removed; using a hosted Postgres (including Supabase Postgres) via DATABASE_URL is still supported.

Fixed / Changed

• Prisma initialization: lib/prisma.ts now lazy-loads PrismaClient only when DATABASE_URL is present to avoid startup errors with Prisma 7 when the env is intentionally empty. Provides a clear error message when Prisma is not initialized.
• BroadcastChannel shim: lib/supabase-mock.ts clarified and renamed internally to a lightweight broadcast shim (keeps supabase export for compatibility). This removes the expectation that the Supabase SDK is required for local realtime features.
• README.md: Removed Supabase-specific deployment instructions and badges. Docker/Local sections now follow the VPS/Server installation flow (see ### 1. VPS/Server) to reduce duplication and keep one canonical deployment path.
• .env.example: Clarified DATABASE_URL guidance and USE_PRISMA behavior for Prisma 7 compatibility.