feat(frontend): replace native controls with styled components

[KyleTryon]

Replace the export dialog’s native filename disclosure with a spring accordion, and replace browser confirmations and native tooltips with controls styled to match Cliparr’s colors, spacing, and corner radius.

• Source removal and subtitle replacement use a shared confirmation dialog. Cancel and Escape preserve existing data, with explicit focus handoff from the subtitle selector and restoration after dismissal.
• App tooltips share one wrapper, support disabled controls, and show only the nearest tooltip on nested timeline handles. Website tooltips support keyboard focus, Escape dismissal, live labels, and Astro navigation.
• The filename accordion preserves form state, hides collapsed fields from keyboard navigation, and respects reduced-motion preferences.

Validation: pnpm preflight on Node 24; frontend and website production builds; browser checks for desktop/mobile layouts, confirm/cancel behavior, selector focus, nested tooltips, timeline keyboard/pointer dragging, tooltip timer cleanup, and live labels.