fix(webapp): use native controls for inline actions (#4698)

## Summary

Replace mouse-only dashboard actions with native buttons.

Copy, remove, and stop-generation controls now expose keyboard focus and
accessible names. Hover-revealed actions remain mounted so keyboard
users can discover them, and a decorative clipboard icon no longer
captures clicks.

Base: [#4697](https://github.com/triggerdotdev/trigger.dev/pull/4697)