Feature/remove sqlite

[0xC0FEBABE]

Implemented Postgres-only cleanup.

Changed:

• Removed SQLite runtime/client switch from src/server/db.ts
• Simplified menu duplicate checks to Postgres case-insensitive Prisma filters in src/server/services/menu.ts
• Removed SQLite test fallback from tests/server/setup.ts and cleanup guard from tests/server/helpers/db.ts
• Deleted:
  • prisma/schema.sqlite.prisma
  • scripts/dev-server-sqlite.mjs
  • scripts/test-server-sqlite.mjs
• Removed SQLite scripts/deps from package.json, pnpm-lock.yaml, pnpm-workspace.yaml
• Updated Prisma generation to generate only prisma/schema.prisma
• Cleaned docs/spec-kit templates/specs/AGENTS/README/env examples to describe PostgreSQL only
• Updated FAIM axiom from postgres + sqlite to postgres and sealed it