feat: add GitHub webhook DTOs with snake_case mapping and header constants

Replace GitHubIssueLabeledWebhookRequest with GitHubIssueRequest.
Add number and repository fields for dedup key construction.
Add Jackson @JsonNaming/@JsonIgnoreProperties for GitHub payload deserialisation.
Add GitHubWebhookHeader constants for webhook header names.

src/main/java/com/onixbyte/deltaforceguide/domain/dto/GitHubIssueLabeledWebhookRequest.java

@@ -1,7 +0,0 @@
-package com.onixbyte.deltaforceguide.domain.dto;
-
-public record GitHubIssueLabeledWebhookRequest(
-        String action,
-        GitHubWebhookIssue issue
-) {
-}

src/main/java/com/onixbyte/deltaforceguide/domain/dto/GitHubIssueRequest.java

@@ -0,0 +1,14 @@
+package com.onixbyte.deltaforceguide.domain.dto;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.annotation.JsonNaming;
+
+@JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
+@JsonIgnoreProperties(ignoreUnknown = true)
+public record GitHubIssueRequest(
+        String action,
+        GitHubWebhookIssue issue,
+        GitHubWebhookRepository repository
+) {
+}

src/main/java/com/onixbyte/deltaforceguide/domain/dto/GitHubWebhookIssue.java

@@ -1,10 +1,17 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.annotation.JsonNaming;
+
 import java.util.List;
 
+@JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
+@JsonIgnoreProperties(ignoreUnknown = true)
 public record GitHubWebhookIssue(
         String url,
         Long id,
+        Long number,
         String title,
         String body,
         List<GitHubWebhookLabel> labels

src/main/java/com/onixbyte/deltaforceguide/domain/dto/GitHubWebhookLabel.java

@@ -1,5 +1,11 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.annotation.JsonNaming;
+
+@JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
+@JsonIgnoreProperties(ignoreUnknown = true)
 public record GitHubWebhookLabel(
         String name
 ) {

src/main/java/com/onixbyte/deltaforceguide/domain/dto/GitHubWebhookRepository.java

@@ -0,0 +1,12 @@
+package com.onixbyte.deltaforceguide.domain.dto;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.annotation.JsonNaming;
+
+@JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
+@JsonIgnoreProperties(ignoreUnknown = true)
+public record GitHubWebhookRepository(
+        String fullName
+) {
+}

src/main/java/com/onixbyte/deltaforceguide/shared/GitHubWebhookHeader.java

@@ -0,0 +1,56 @@
+package com.onixbyte.deltaforceguide.shared;
+
+/**
+ * This class lists the header names that GitHub sends in webhook requests.
+ *
+ * @author siujamo
+ */
+public class GitHubWebhookHeader {
+
+    /**
+     * The unique identifier of the webhook.
+     */
+    public static final String HOOK_ID = "X-GitHub-Hook-ID";
+
+    /**
+     * The name of the event that triggered the delivery.
+     */
+    public static final String EVENT = "X-GitHub-Event";
+
+    /**
+     * A globally unique identifier (GUID) to identify the event.
+     */
+    public static final String DELIVERY = "X-GitHub-Delivery";
+
+    /**
+     * This header is sent if the webhook is configured with a {@code secret}. This is the HMAC hex
+     * digest of the request body, and is generated using the SHA-1 hash function and the secret as
+     * the HMAC {@code key}. {@code X-Hub-Signature} is provided for compatibility with
+     * existing integrations. We recommend that you use the more secure
+     * {@code X-Hub-Signature-256} instead.
+     */
+    public static final String SIGNATURE = "X-Hub-Signature";
+
+    /**
+     * This header is sent if the webhook is configured with a {@code secret}. This is the HMAC hex
+     * digest of the request body, and is generated using the SHA-256 hash function and the
+     * {@code secret} as the HMAC key. For more information, see <a href="https://docs.github.com/en/webhooks/using-webhooks/securing-your-webhooks"
+     * >Validating webhook deliveries</a>.
+     */
+    public static final String SIGNATURE_256 = "X-Hub-Signature-256";
+
+    /**
+     * This header will always have the prefix {@code GitHub-Hookshot/}.
+     */
+    public static final String USER_AGENT = "User-Agent";
+
+    /**
+     * The type of resource where the webhook was created.
+     */
+    public static final String INSTALLATION_TARGET_TYPE = "X-GitHub-Hook-Installation-Target-Type";
+
+    /**
+     * The unique identifier of the resource where the webhook was created.
+     */
+    public static final String INSTALLATION_TARGET_ID = "X-GitHub-Hook-Installation-Target-ID";
+}