Server error codes audit

[begelundmuller]

• Consistently differentiate between not found and forbidden errors
• Defer status code mapping to error handling middleware when possible
• Audit server error handling for consistency and correctness

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[pjain1]

I tried checking but looks like no logic depends on the returned status codes, as long as its the case this looks fine.