[Core] Implement Multi-tenancy

[NeftaliYagua]

📋 Description

Implement multi-tenant architecture with tenant isolation at database and application level.

Story Points: 13 SP
Sprint: Sprint 2 (Jan 16-29, 2026) - IN PROGRESS
Estimated Duration: 5 days
Risk Level: High (Data isolation critical for security)
Dependencies: #1 (Authentication must be completed first)

✅ Acceptance Criteria

• Tenant identification mechanism (subdomain or header-based)
• Database-per-tenant or schema-per-tenant strategy implemented
• Tenant context middleware configured
• Tenant provisioning API endpoints
• Data isolation verified (no cross-tenant data access)
• Tenant-specific configuration storage
• Connection string management per tenant
• Tenant onboarding workflow
• Admin panel for tenant management
• Migration scripts for tenant databases
• Security audit for tenant isolation
• Load testing with multiple tenants

🔧 Technical Notes

• Strategy: Schema-per-tenant (cost-effective for <100 tenants)
• Tenant identifier: Subdomain (tenant1.prodaric.com) or X-Tenant-ID header
• EF Core with TenantId global query filter
• Connection pooling per tenant
• Migration: Automatic schema creation on tenant signup
• Backup: Tenant-specific backup schedules

📦 Subtasks

• Design multi-tenancy architecture (DB strategy)
• Implement tenant identification middleware
• Configure EF Core with tenant context
• Create tenant provisioning endpoints
• Setup connection string management
• Implement data isolation filters
• Create tenant migration scripts
• Build admin panel for tenant management
• Write tenant isolation tests
• Security review (penetration testing)
• Load testing with 50+ concurrent tenants

🔗 Related

• Depends on [Core] Setup Authentication System #1 (Auth required for tenant context)
• Part of Sprint 2 (43 SP total capacity)
• Critical for v0.1.0 milestone
• See ROADMAP.md Sprint 2 section