openai/gpt-chat-latest → A (3:2)

Side A introduces a reusable `get-base-url` utility driven by `HOSTNAME` with environment fallbacks, replaces multiple hardcoded callback URL implementations across OAuth/login integrations, updates the frontend to use `window.location.origin`, and adjusts deployment to the staging branch. These changes fix incorrect redirects for custom hosts and centralize configuration, whereas Side B mainly corrects vote comparison highlighting and visualization logic with supporting tests and CSS, an important but more localized UI fix.