Clarify issue comment semantics and strengthen report_progress guidance (#292)

- Add `comment_type: "issue"` to `IssueCommentCreatedEvent` interface and
  dispatch sites so agents can distinguish issue comments from PR review
  comments
- Add dedicated "Progress reporting" section to system prompt making
  `report_progress` the mandatory tool for sharing results
- Update `reply_to_review_comment` description to clarify it only works
  for inline review comments on PR diffs, not issue comments

Co-authored-by: pullfrog[bot] <226033991+pullfrog[bot]@users.noreply.github.com>

mcp/comment.ts

@@ -329,7 +329,7 @@ export function ReplyToReviewCommentTool(ctx: ToolContext) {
   return tool({
     name: "reply_to_review_comment",
     description:
-      "Reply to a PR review comment thread. Call this for EACH comment you address. Keep replies extremely brief (1 sentence max).",
+      "Reply to a PR review comment thread (NOT issue comments — this only works for inline review comments on PR diffs). Call this for EACH comment you address in AddressReviews mode. Keep replies extremely brief (1 sentence max).",
     parameters: ReplyToReviewComment,
     execute: execute(async ({ pull_number, comment_id, body }) => {
       const bodyWithFooter = await addFooter(ctx, body);