Get Build Logs

Proxy the log body for a build, source-faithfully.

Fetches the log content from Build Coordinator and returns it as text/plain; charset=utf-8 without modification. No escape stripping, no control-byte filtering, no timestamp injection. Terminal-escape handling is the CLI consumer's responsibility. The only hygiene applied is at the coordinator client layer: valid UTF-8 output and a size-capped read. No JSON envelope; the body is the log.

Returns: 200 with the log body. 404 if the build does not exist, has no Build Coordinator counterpart (task_id IS NULL), or the coordinator itself returns 404. 500 if an unexpected error occurs (e.g. get_build_by_id raises). 502 if Build Coordinator is unreachable or returns a 5xx error.