fix: add rate limiting to download counter to prevent inflation

[orlyjamie]

Summary

• Add IP-based rate limiting (5 downloads per skill per IP per hour) to prevent download count inflation
• Only trust cf-connecting-ip header - x-forwarded-for is trivially spoofable
• Still serve files to rate-limited users, just don't count inflated downloads

The Vulnerability

The download endpoint at convex/downloads.ts:56 incremented download counts with no rate limiting. An
attacker could inflate any skill's download count by:

  for i in {1..1000}; do                                                                                      
    curl -H "X-Forwarded-For: 1.2.3.$i" \                                                                     
      "https://api.clawdhub.com/download?slug=target-skill" -o /dev/null                                      
  done    

Important Note

Download counts are fundamentally gameable as trust metrics because downloads are anonymous. Even with
rate limiting, attackers can use proxies/VPNs/Tor.

Recommendation: De-emphasize downloads in the UI. Stars and installs are better trust signals because they
require authenticated sessions.

Reference: https://x.com/theonejvo/status/2015892980851474595

[vercel]

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[orlyjamie]