Timezone selector only shows GMT offsets — cannot search by city name

## Current behavior The timezone selector in Preferences (and Profile) settings only displays GMT offset labels (e.g. "GMT-5", "GMT+1") in the dropdown. Users cannot search by city name (e.g. typing "Toronto" or "Montreal"). The underlying data uses IANA timezone identifiers (like `America/Toronto`), but the native `<datalist>` element renders differently across browsers: - **Chrome/Edge**: Shows both the IANA name and GMT offset — city search works. - **Firefox/Safari**: Only shows the GMT offset label — city search does not work. ## Expected behavior 1. **City-name search should work in all browsers** — the dropdown should visibly display IANA timezone names (e.g. "America/Toronto (GMT-5)") so users can search by city regardless of browser. 2. **Browser timezone as default** — when no timezone is set, the selector should default to the user's browser/OS timezone (`Intl.DateTimeFormat().resolvedOptions().timeZone`) instead of being blank. 3. **Extended city search** — consider mapping common city names that are not part of IANA identifiers (e.g. "Montreal" → "America/Toronto", "Rome" → "Europe/Rome") so users can search by their actual city, not just the IANA representative city. ## Steps to reproduce 1. Go to Settings → Preferences 2. Click the Timezone input 3. Try typing a city name like "Toronto" or "Montreal" 4. Observe that only GMT offsets appear in the dropdown (browser-dependent) ## Environment - Affected browsers: Firefox, Safari (Chrome works partially) - Page: /settings/preferences