backend: add basic logging middleware

[scott-cohere]

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• PR title: "area: description"
  • Where "area" is whichever of interface, frontend, model, tools, backend, etc. is being modified. Use "docs: ..." for purely docs changes, "infra: ..." for CI changes.
  • Example: "deployment: add Azure model option"

Adds a simple logging middleware to Fast API app.

Tested locally

• Add tests and docs: Please include testing and documentation for your changes
• Lint and test: Run make lint and make run-tests

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