Add proxy rotation to Steam inventory fetching to prevent rate limits

- Install https-proxy-agent package
- Add 1000 residential proxy list for round-robin rotation
- Implement proxy support in getSteamInventory() function
- Fix intermittent HTTP 429 rate limit errors from Steam Community API
- Enable reliable inventory fetching for onboarding flow

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: rainerstudios