Add POST endpoint to create new merchants via admin API

Enables merchant creation through the admin UI by adding a POST endpoint to MerchantAdminController. Also adds avantlinkMid field to MerchantAdminDto to satisfy the required database constraint.

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

src/main/java/group/goforward/battlbuilder/controllers/api/v1/admin/MerchantAdminController.java

@@ -3,6 +3,7 @@ package group.goforward.battlbuilder.controllers.api.v1.admin;
 
 import org.springframework.web.bind.annotation.CrossOrigin;
 import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.PutMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestBody;
@@ -30,6 +31,19 @@ public class MerchantAdminController {
         return merchantRepository.findAll().stream().map(this::toDto).toList();
     }
 
+    @PostMapping
+    public MerchantAdminDto createMerchant(@RequestBody MerchantAdminDto payload) {
+        Merchant merchant = new Merchant();
+        merchant.setName(payload.getName());
+        merchant.setAvantlinkMid(payload.getAvantlinkMid());
+        merchant.setFeedUrl(payload.getFeedUrl());
+        merchant.setOfferFeedUrl(payload.getOfferFeedUrl());
+        merchant.setIsActive(payload.getIsActive() != null ? payload.getIsActive() : true);
+
+        merchant = merchantRepository.save(merchant);
+        return toDto(merchant);
+    }
+
     @PutMapping("/{id}")
     public MerchantAdminDto updateMerchant(
             @PathVariable Integer id,
@@ -51,6 +65,7 @@ public class MerchantAdminController {
         MerchantAdminDto dto = new MerchantAdminDto();
         dto.setId(m.getId());
         dto.setName(m.getName());
+        dto.setAvantlinkMid(m.getAvantlinkMid());
         dto.setFeedUrl(m.getFeedUrl());
         dto.setOfferFeedUrl(m.getOfferFeedUrl());
         dto.setIsActive(m.getIsActive());

src/main/java/group/goforward/battlbuilder/web/dto/merchant/MerchantAdminDto.java

@@ -6,6 +6,7 @@ import java.time.OffsetDateTime;
 public class MerchantAdminDto {
     private Integer id;
     private String name;
+    private String avantlinkMid;
     private String feedUrl;
     private String offerFeedUrl;
     private Boolean isActive;
@@ -28,6 +29,14 @@ public class MerchantAdminDto {
         this.name = name;
     }
 
+    public String getAvantlinkMid() {
+        return avantlinkMid;
+    }
+
+    public void setAvantlinkMid(String avantlinkMid) {
+        this.avantlinkMid = avantlinkMid;
+    }
+
     public String getFeedUrl() {
         return feedUrl;
     }