Add centralized issue discovery homepage

[FrancisPhan0105]

Fixes #43.

Summary

• Replace the homepage with a centralized Pvium bounty issue discovery page.
• Move the existing deployment/setup homepage to /deploy.
• Store GitHub issue metadata on bounty records and keep it updated from issue webhooks.
• Support recent/top browsing, bounty minimum filtering, sort order controls, status, dates, excerpts, repo names, payout amounts, and GitHub issue links.

Notes

• Recent sorting uses issue metadata with a bounty updatedAt fallback so older rows without metadata do not float above real recent issues.
• Display status prioritizes the app bounty status when it is no longer OPEN, so paid/cancelled records are not hidden by a still-open GitHub issue state.
• The discovery controls use regular buttons/selects instead of an incomplete ARIA tabs pattern.

Validation

• npm run prisma:generate
• npm run typecheck
• npm test
• npm run build
• git diff --check

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