revamp and upgrade to modern stack

[ashwin31]

Summary by CodeRabbit

• New Features

  • Case management and Knowledge Base (Solutions)
  • Teams, Contacts, Accounts, Opportunities, Invoices with products & line‑items
  • Email scheduling/logging and org-scoped background tasks
  • Organization switching and org-scoped APIs

• Security

  • Row‑Level Security (DB-level org isolation)
  • Comprehensive security audit logging and tightened org permissions

• Documentation

  • Expanded backend README with architecture and setup guidance

• Tests

  • Multi‑tenancy and RLS integration test suite added

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