docs: add comprehensive API error reference documentation
Document all error response formats (OpenAI, Anthropic, Open Responses),
HTTP status codes, per-endpoint error scenarios, and client error handling
examples based on actual error handling code in the codebase.
Signed-off-by: localai-bot <localai-bot@noreply.github.com>
Co-authored-by: localai-bot <localai-bot@noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
