Improve API error handling in CLI deploy command

[chronark]

API error handling in the CLI currently prints the raw error response directly to the terminal.

Example output when running a deploy command:

❯ go run . deploy --project-id="proj_5VogF2BSh3aZAFZ6" --context="./demo_api" --api-base-url="http://localhost:7070" --root-key="unkey_8JT24f1meaF3cxzF2WfAhn" --env=production

✘ Failed to upload build context
  => {"meta":{"requestId":"req_5Vogt5YzbRmMDF51"},"error":{"detail":"Missing one of these permissions: ['{ project.**.generate_upload_url []}', '{ project.proj_5VogF2BSh3aZAFZ6.generate_upload_url []}'], have: [...]","status":403,"title":"Insufficient Permissions"}}

Improve this so the CLI surfaces a clearer, more user-friendly error message instead of dumping the full JSON response.

[linear]

ENG-2414