refactor: migrate Bucket4j to lambda-based builder API

Replace deprecated Bandwidth.classic() with new builder pattern:
- Remove Bandwidth and Refill imports (no longer needed)
- Use lambda-based .addLimit() with fluent API
- Change: Bandwidth.classic(capacity, Refill.greedy(...))
- To: .addLimit(limit -> limit.capacity(...).refillGreedy(...))

This eliminates the last compilation warning and aligns with
Bucket4j 8.10.1+ recommended API (deprecated since 8.5.0).

All 550 tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: KhaledSalhab-Develeap

src/main/java/com/jhf/coupon/security/RateLimitingFilter.java

@@ -1,9 +1,7 @@
 package com.jhf.coupon.security;
 
 import com.jhf.coupon.config.RateLimitProperties;
-import io.github.bucket4j.Bandwidth;
 import io.github.bucket4j.Bucket;
-import io.github.bucket4j.Refill;
 import jakarta.servlet.FilterChain;
 import jakarta.servlet.ServletException;
 import jakarta.servlet.http.HttpServletRequest;
@@ -128,12 +126,11 @@ private Bucket resolveBucket(String clientIp, Map<String, Bucket> bucketMap, int
      * @return New Bucket instance
      */
     private Bucket createNewBucket(int requestsPerMinute) {
-        Bandwidth limit = Bandwidth.classic(
-                requestsPerMinute,
-                Refill.greedy(requestsPerMinute, Duration.ofMinutes(1))
-        );
         return Bucket.builder()
-                .addLimit(limit)
+                .addLimit(limit -> limit
+                        .capacity(requestsPerMinute)
+                        .refillGreedy(requestsPerMinute, Duration.ofMinutes(1))
+                )
                 .build();
     }