fix: handle missing comment payload in Forgejo pull_request_review_comment

Forgejo's pull_request_review_comment event does NOT include a top-level
`comment` object in the webhook payload. This caused crashes at:
- create-initial.ts: context.payload.comment.id (for reply-to-review)
- fetcher.ts: context.payload.comment.created_at (for trigger timestamp)

Fix: use optional chaining and fall back gracefully — reply-to-review
becomes a regular issue comment, trigger timestamp returns undefined.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/github/data/fetcher.ts

@@ -40,7 +40,8 @@ export function extractTriggerTimestamp(
   } else if (isPullRequestReviewEvent(context)) {
     return context.payload.review.submitted_at || undefined;
   } else if (isPullRequestReviewCommentEvent(context)) {
-    return context.payload.comment.created_at || undefined;
+    // Forgejo's pull_request_review_comment payload may lack the `comment` object
+    return (context.payload as any).comment?.created_at || undefined;
   }
 
   return undefined;

src/github/operations/comments/create-initial.ts

@@ -77,14 +77,26 @@ export async function createInitialComment(
         });
       }
     } else if (isPullRequestReviewCommentEvent(context)) {
-      // Only use createReplyForReviewComment if it's a PR review comment AND we have a comment_id
+      // Only use createReplyForReviewComment if we have a comment_id.
+      // Forgejo's pull_request_review_comment payload lacks the top-level
+      // `comment` object, so fall back to a regular issue comment there.
+      const reviewCommentId = (context.payload as any).comment?.id;
+      if (reviewCommentId) {
         response = await octokit.rest.pulls.createReplyForReviewComment({
           owner,
           repo,
           pull_number: context.entityNumber,
-        comment_id: context.payload.comment.id,
+          comment_id: reviewCommentId,
           body: initialBody,
         });
+      } else {
+        response = await octokit.rest.issues.createComment({
+          owner,
+          repo,
+          issue_number: context.entityNumber,
+          body: initialBody,
+        });
+      }
     } else {
       // For all other cases (issues, issue comments, or missing comment_id)
       response = await octokit.rest.issues.createComment({