Redesign Informational schedule row with centered notice treatment

[JacobCoffee]

Summary

• Replaces the flat gray "Informational" track-item for announcements like "Swag Pickup Closes" with a centered, tinted notice row on the schedule.
• Drops the "Informational" track-badge text in favor of an inline information icon.
• Uses the existing `--pycon-accent` token (purple in light, pink in dark) so the row reads as branded in both themes without needing a per-theme layout branch.
• Row stays compact so multiple notices stack cleanly on a day (e.g. Sat 8:00 am with three back-to-back notices) without overwhelming the list.

Before → After: the row that used to read "Swag Pickup Closes / Informational / 1:30 pm" on a dark-gray bar now reads "ⓘ Swag Pickup Closes / 🕐 1:30 pm" centered on a soft brand-tinted bar.

Test plan

• Light mode: informational rows show a soft purple tint, icon + title centered on one line, time centered beneath
• Dark mode: informational rows show a soft pink tint, same layout
• Stacked notices (multiple back-to-back, e.g. Registration Desk Opens + Open Spaces Rooms Open + Expo Hall Opens on the same day) look consistent — icons align, rows feel like a rhythm not a billboard
• Non-informational sessions render unchanged
• Tapping a notice still navigates to its detail page
• `prefers-reduced-motion` still works (transition is a simple bg fade only)

[JacobCoffee]