All JS modules were running immediately (IIFE/DOMContentLoaded) but
tab HTML is lazy-loaded from /components/*.html, causing null errors
on every addEventListener call. Each module now listens for tabChanged
with its tab name and initializes once after the DOM is ready.
Also: quiz question/explanation boxes changed to textarea for
multi-line support; quiz display uses sanitizeHtml() so formatted
text (bold, lists, etc.) renders correctly.
Adds setOutputText() helper that escapes HTML and converts \n to <br>,
applied to all AI-generated note outputs so line breaks are preserved
in contenteditable divs. Also cleans up CSS for quiz option markers.
