Feat(ai-gateway): Add model/provider access controls on virtual keys

[Br0wnHammer]

Describe your changes

• Adds 4 new fields to virtual keys — allowed_models, blocked_models, allowed_providers, blocked_providers — enabling admins to restrict which models and providers a key can access
• Enforces ACLs at proxy time with 403 responses, supporting wildcard patterns (e.g. claude-haiku*)
• Includes frontend fields in the create modal and ACL chips on key cards

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