feat(m10): add audit retention policy configuration

services/delivery-platform-api/src/main/java/cn/craftlabs/platform/api/audit/AuditController.java

@@ -18,6 +18,7 @@ import org.springframework.web.bind.annotation.RestController;
 import java.nio.charset.StandardCharsets;
 import java.time.LocalDate;
 import java.util.List;
+import java.util.Map;
 
 @RestController
 @RequestMapping("/api/v1/audit-events")
@@ -77,6 +78,14 @@ public class AuditController {
                 .body(resource);
     }
 
+    @GetMapping("/retention-config")
+    public ResponseEntity<Map<String, Object>> getRetentionConfig() {
+        return ResponseEntity.ok(Map.of(
+            "retentionDays", 365,
+            "autoCleanup", false
+        ));
+    }
+
     private static String escapeCsv(String value) {
         if (value == null) return "";
         if (value.contains(",") || value.contains("\"") || value.contains("\n")) {