fix: restore rate limiting and fix language switch links

Security:
- Restore PDF endpoint rate limiting (3 requests/minute)
- Keep security headers middleware (CSP, HSTS, X-Frame-Options)
- Keep origin checker for PDF endpoint
- Restore recovery and logger middleware

Links:
- Fix 'CV in [language]' links to use relative URLs (/?lang=)
- Now correctly navigates to page instead of downloading
- PDF download links remain as full URLs for direct download

Simplifications:
- Remove unused advanced middleware (not yet implemented)
- Use simpler 2-parameter rate limiter constructor
- Remove unused strconv import

main.go

@@ -75,6 +75,7 @@ func main() {
 	// Create rate limiter for PDF endpoint
 	// Allow 3 PDF generations per minute per IP
 	pdfRateLimiter := middleware.NewRateLimiter(3, 1*time.Minute)
+	log.Printf("🔒 Rate limiter enabled for PDF endpoint (3 requests/minute)")
 
 	// Routes
 	mux.HandleFunc("/", cvHandler.Home)