feat: improve mobile responsiveness of admin dashboard tables (Closes #235)

[waterWang]

Summary

This PR improves the mobile responsiveness of the admin dashboard tables by introducing a reusable ResponsiveTable component that transforms traditional HTML tables into a stacked card layout on mobile viewports.

Changes

New component

• components/ui/responsive-table.tsx — A wrapper component that provides responsive table behavior. On screens narrower than sm (640px), table rows collapse into stacked cards with labeled fields.

Updated pages

• app/[communitySlug]/admin/page.tsx — Webhook Events table now uses ResponsiveTable with data-label attributes for mobile field labels
• app/analytics/page.tsx — Strategy Pools table now uses ResponsiveTable with data-label attributes for mobile field labels

CSS

• app/globals.css — Added responsive table styles that:
  • Hide the table header on mobile (screen-reader accessible)
  • Display each row as a bordered card with rounded corners
  • Show field labels via ::before pseudo-elements using data-label attributes
  • Preserve full desktop layout above the sm breakpoint

Acceptance Criteria

• ✅ Both admin tables are fully usable (no horizontal scroll, readable text) at a 375px viewport width
• ✅ Desktop table layout is unchanged above the breakpoint
• ✅ No horizontal scrolling required on mobile
• ✅ All existing tests pass