Ticket #135 extension - Added comment support to researcher reviewed tracking: Added `researcher_reviewed_at` column to comments table with index. Updated `list_comments` MCP tool to support `reviewed_before` filter (same pattern as tickets/memories). Extended `mark_as_reviewed` tool to support "comment" type. Added `list_comments` and `add_comment` to researcher role permissions in mcp_permissions.yml. Added 7 new test cases, all 92 tests passing.