feat(LiveComponents.TripPlannerForm): fixes for mode selector + updated MbtaMetro & overhauled typography

[thecristen]

Summary of changes

Asana Ticket: TP UI | Inputs | Polished accessibility selector and TP UI | Inputs | Polished mode selector

Technically not 100% polished yet since these don't yet use the official design system tokens for colors and spacing. These are pretty close.

Sorry for the omnibus PR! 😅 But the recent updates to MbtaMetro included CSS I wanted to incorporate here, including:

• Updated font files (which I've downloaded here, replacing our current font files). This should fix the current issue on dev (where it can't find the Inter font and thus falls back to Helvetica)
• Updated header styles. They're a 99.9% match of what's already on the site, with much simpler CSS.
  These let me start phasing out a whole bunch of our homegrown utility files... which accounts for most of this PR diff. This phaseout is not even close to complete but is enough for now. I've checked many pages to ensure I'm not introducing style regressions!
• Our tailwind config now uses the @tailwindcss/forms plugin in full, including its style resets. This required some edits to our custom <select> styling to avoid showing multiple carets.
• Our tailwind config now uses important: true as the forms plugin is kinda buggy otherwise, since it inserts its reset CSS in a way that overwrites our own styles. 🙄
• Adds extra configuration to LiveSocket, to avoid <details> open state changing inside a LiveView.