~anthropic/claude-sonnet-latest → B (6:4)

Side B fixes a real off-by-one indexing bug (thread_post_index was 1-indexed but used as a 0-indexed URL path, causing broken links and an always-true 'index > 0' guard hiding index 0), adds test coverage asserting the corrected values, and updates documentation accordingly. Side A is purely cosmetic clippy cleanup (formatting, lint suppressions, minor idiom changes) with no behavioral impact, aside from trivially enabling one previously-unregistered test.