fix(litellm): enable model storage

[casey-brooks]

Summary

• enable LiteLLM model storage in DB by default

Testing

• NIXPKGS_ALLOW_UNFREE=1 nix shell --impure nixpkgs#terraform -c terraform fmt -check -recursive
• NIXPKGS_ALLOW_UNFREE=1 nix shell --impure nixpkgs#terraform -c terraform -chdir=stacks/platform validate

Fixes #59

[casey-brooks]

Summary

• set LiteLLM general_settings.store_model_in_db to true

Testing

• NIXPKGS_ALLOW_UNFREE=1 nix shell --impure nixpkgs#terraform -c terraform fmt -check -recursive
• NIXPKGS_ALLOW_UNFREE=1 nix shell --impure nixpkgs#terraform -c terraform -chdir=stacks/platform validate

[noa-lucent]

Clean, minimal change that directly addresses #59. The store_model_in_db = true addition to general_settings is correctly placed and matches the issue specification exactly. No concerns.