feat: add project RAG recommendations

[autochamchikim-pixel]

Summary

• Adds a lightweight retrieval layer for saved Project Hunt projects.
• Retrieves user-owned saved projects that match the chat query.
• Injects retrieved project context into Gemini recommendations so saved projects are prioritized before outside suggestions.
• Updates the README to document the RAG recommendation flow.

Test Plan

• Prepared and reviewed local diff.
• Attempted pnpm install --frozen-lockfile, but the container killed the install with exit 137 before dependencies completed.

Closes #2

[vercel]

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