[Feat] Issue-1063 Add Upstash-backed rate limiting

[Dhirenderchoudhary]

Description

Closes #1063

This PR improves rate limiting for the Vercel/serverless deployment by replacing in-memory rate limit counters with Upstash Redis-backed IP rate limiting.

Changes included:

• Centralized reusable rate limit policies.
• Added Upstash-backed store for express-rate-limit.
• Kept existing limits:
  • /api/logo/* → 100 req/min
  • other main API routes → 60 req/min
• Added dedicated auth and upload/signed-url limiters.
• Added consistent JSON 429 responses.
• Added proxy trust config for Vercel client IP handling.
• Added env validation for required Upstash config.
• Added tests for rate limit behavior and env validation.

Closes #1063

What type of PR is this? (Check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📄 Documentation Update
• 👨‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🛠️ CI/CD

Screenshots (if applicable)

Not applicable.

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud