Replace hard-coded white/light colors with dark theme palette matching the rest
of the app. Key changes: dark navy background (#1e293b/#0f172a), high-contrast
text (#f1f5f9 titles, #94a3b8 body), teal accent (#14b8a6) for active filter and
unread left-border, red (#f87171) clear button, dark scrollbar, subtle hover
states on items and action buttons.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
