feat: add output truncation and offset paging to all large-output tools

- coding_tools: list_files (max_entries=200, sorted), run_command
  (max_chars=8000, output_offset), grep_search (max_lines=100, offset);
  added _truncate_output helper for run_command paging
- pr_tools: get_pull_request_diff / get_pull_request_patch now truncate
  at 15k chars with hunk-boundary awareness and char_offset paging;
  get_pull_request_comments gains limit/offset paging
- issue_tools: get_issue_comments gains limit/offset paging
- file_tools: get_file_content / get_file_content_with_ref now paginate
  by line (offset=1, limit=250), matching existing read_file convention;
  added _paginate_lines helper
- research_tools: fetch_url gains char_offset parameter; _smart_truncate
  now slices from an offset and embeds next char_offset in the footer
- gitea_tools facade: all new params threaded through

gitea/tools/issue_tools.py

@@ -26,10 +26,34 @@ class IssueTools:
         except Exception as e:
             return f"Error closing issue: {str(e)}"
 
-    def get_issue_comments(self, owner: str, repo: str, issue_number: int) -> str:
+    def get_issue_comments(
+        self,
+        owner: str,
+        repo: str,
+        issue_number: int,
+        limit: int = 20,
+        offset: int = 0,
+    ) -> str:
+        """Get comments on an issue with optional paging.
+
+        Args:
+            limit: Maximum number of comments to return (default 20).
+            offset: Zero-based comment index to start from (default 0).
+        """
         try:
-            comments: list[CommentModel] = self._client.get_issue_comments(owner, repo, issue_number)
-            return json.dumps([c.model_dump() for c in comments], indent=2)
+            comments: list[CommentModel] = self._client.get_issue_comments(
+                owner, repo, issue_number
+            )
+            total: int = len(comments)
+            page: list[CommentModel] = comments[offset : offset + limit]
+            result: str = json.dumps([c.model_dump() for c in page], indent=2)
+            if total > offset + limit:
+                next_offset: int = offset + limit
+                result += (
+                    f"\n\n[{total} comments total — showing {offset}–{offset + len(page)}. "
+                    f"Re-call with offset={next_offset} to see more.]"
+                )
+            return result
         except Exception as e:
             return f"Error getting issue comments: {str(e)}"