The InsertLink light dialog has a typo in the for attribute of the URL label, causing a case mismatch with the input's id. This results in accessibility tools like Wave and SortSite reporting the URL textbox as an unlabeled control.
Steps to Reproduce
1. Add a RadEditor with EnableAriaSupport="true" to a page
2. Ensure the InsertLink tool is enabled (it is by default)
3. Click the InsertLink toolbar button to open the dialog
4. Run an accessibility audit using Wave, SortSite, or inspect the DOM

Expected Behavior
The label's for attribute should match the input's id attribute exactly, allowing accessibility tools to correctly associate the label with the input.

Actual Behavior
• Label has for="LinkURL" (uppercase "URL")
• Input has id="LinkUrl" (mixed case "Url")
Since HTML for/id matching is case-sensitive, the label is not properly associated with the input control.

Affected File
InsertLink.ascx