Frontend: Submit CTA (prefilled GitHub issue) + responsive polish

[Jose-Gael-Cruz-Lopez]

Context

Close the loop back to the repo + final ship-quality polish. Depends on #14; best done after #16–#18 exist.

What to build

• Submit CTA: header button → prefilled GitHub issue:
  https://github.com/Jose-Gael-Cruz-Lopez/hackhq/issues/new?template=link_only.yaml
  (reinforces the "site ↔ repo" link; moderation stays in GitHub).
• Header GitHub repo link + star nudge.
• Responsive: globe scales on mobile; filters/virtual panel collapse into a drawer/sheet on small screens.
• States: loading skeleton (while Frontend: Supabase data layer (client, types, fetch) #15 fetches), error state, empty state.

Acceptance

• Submit button opens the prefilled GitHub issue template
• Repo link present; layout works on mobile + desktop
• Loading / error / empty states are polished
  Depends on: Frontend: Scaffold Vite + React + TS + Tailwind app (site/) #14 (+ Frontend: 3D globe with status-colored markers (react-globe.gl) #16–Frontend: Search, filters, and Virtual/Online side panel #18 for full polish)

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Part of #10 · Design spec · Repo data lives in .github/scripts/listings.json