htmx 4.0.0 brings morph swaps and migration changes

htmx 4.0.0 makes attribute inheritance opt-in by default, so parent attributes now need an ':inherited' suffix to apply to child elements.

The release also standardizes event names, moves internal requests from XMLHttpRequest to fetch(), and re-fetches history entries instead of using localStorage snapshots by default.

New additions include built-in morph swaps, the 'hx-partial' element, new extensions, and an upgrade checker for htmx 2 projects.