Web: drop guessType, update type enum to 6-type taxonomy

The memory type system has been updated from four legacy types (decision, asset, fact, context) to six named types — Decision, How-to, Standard, Fact, Event, and Note — plus an Auto state that lets the backend classify the memory. The composer and New Memory dialog no longer show a flipping predicted label ("Auto · Fact") on every keystroke; the button simply reads "Auto" while no explicit type is chosen.