Implement caching for bounty listings and recommendations

[bishopBethel]

Add Redis caching to bounty listing (5 min TTL) and recommendation (15 min TTL) endpoints. Invalidate on bounty status changes and tech stack updates.

[willkhinz]

On it! I'm preparing a fix now and will open a PR in a few minutes.

[willkhinz]

I have opened a Pull Request with the fix here: #130

Thanks!