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

Side B implements a real URL-routing refactor (item paths become canonical /~/<url> routes) with new tests validating parsing and rendering, plus removes dead theme-switching code and consolidates CSS—substantive structural improvement with test coverage. Side A is a useful but narrower bugfix (deploy target and base-URL centralization) that fixes real redirect bugs but is smaller in scope and lacks new tests.