openai/gpt-chat-latest → A (9:1)

Side A makes a semantic correctness change by treating `thread_post_index` as a guaranteed 0-based index, replacing silent `unwrap_or(0)` fallbacks with `expect(...)`, always rendering the post link, updating API/docs to distinguish 0-based URL indices from 1-based feed ordinals, and adding integration tests to lock in the behavior. Side B is overwhelmingly workspace-wide rustfmt reformatting plus tooling/editor configuration (pinning rustfmt/clippy, VS Code settings, minor CSS cleanup), with little lasting change to project behavior.