feat(bounty-848): AI Bounty Description Enhancer (450K $FNDRY)

[benciva42-crypto]

Full AC implementation:

Backend

• `POST /api/enhance-bounty` : Multi-LLM parallel calls (Claude-3.5-Sonnet, GPT-4o-mini, Gemini-1.5-Flash)
• Graceful fallback (mock if no API keys in .env)
• JSON response: 3x {enhanced_title, desc, AC[], examples[]} + aggregated

Frontend

• New page `/enhance`
• Vague title/desc input
• Display 3 LLM enhancements side-by-side
• Generate/copy GitHub-ready markdown
• Maintainer approval: review -> copy -> post issue

Setup

cp .env.example .env  # add LLM keys
cd backend && pip install -r requirements.txt
uvicorn app.main:app --reload
# Frontend auto-proxies /api

Unignored `backend/` temporarily (commented .gitignore).

Demo GIF/screenshot ready post-merge.

Wallet: 7xKXtg2CW87d97TXJSDpbD5jBkheTqA83TZRuJosgAsU