batch: security fixes - rate limiting, svg sanitization, retry logic, request dedup

[saurabhhhcodes]

Closes #218, #215, #220, #197

Security:

• [Security] No rate limiting on badge generation endpoints - GitHub API exhaustion and DoS possible #218: Add in-memory rate limiter middleware (30 req/min per IP) for badge generation endpoints
• [Security] SVG badge generation uses direct string interpolation - stored XSS via malicious GitHub usernames/repo names #215: Sanitize wrapSvg title/description to prevent XSS via SVG injection
• [SECURITY] Implement Request Deduplication and Cache Consistency for External Data Fetching #197: Deduplicate concurrent GitHub API requests for the same username (reduces load/spam)
• [Security] GitHub API token leaked in error responses and potentially in logs #217: Prune error detail from error SVG to avoid leaking internal info

Reliability:

• fix: Add request timeout and retry logic for Codeforces and CodeChef APIs #220: Add exponential-backoff retry (2 attempts) to Codeforces and CodeChef API calls

Co-authored-by: none

[vercel]

Someone is attempting to deploy a commit to the Dot_NotSam's projects Team on Vercel.

A member of the Team first needs to authorize it.