Add centralized issue discovery homepage

[Jorel97]

Closes #43

Summary

• move the existing Pvium setup/deploy homepage to /deploy
• replace / with a centralized issue discovery dashboard for bounty issues across connected repositories
• add recent/top sorting, ascending/descending ordering, and a minimum bounty filter
• persist GitHub issue metadata from bounty-label webhooks so cards can show title, URL, state, excerpt, and issue timestamps
• add a Prisma migration for issue metadata fields and focused tests for discovery filtering/sorting/excerpts

Verification

• node --disable-warning=ExperimentalWarning --experimental-transform-types --test tests/*.test.ts (20 passing)
• node --check src/lib/issues/discovery.ts

Note: this environment does not include npm, so I could not run npm run typecheck or npm run build locally. The app's Vercel build runs prisma migrate deploy && prisma generate && next build, which will regenerate Prisma types from the updated schema before building.

[vercel]

@Jorel97 is attempting to deploy a commit to the Bytegum Team on Vercel.

A member of the Team first needs to authorize it.