file: URLs on UNC shares are not supported

### Windows Terminal version

1.21.3231.0

### Windows build number

10.0.26100.2894

### Other Software

_No response_

### Steps to reproduce

1. Output a formatted file URL for a file stored on a UNC network share. e.g. file://qnap-fs/dvd/test.txt
2. Note that there is an underline beneath the URL when you mouse hovers over it
3. Ctrl+Left mouse click the URL

### Expected Behavior

1. The associated program runs with the file as an argument, or the Open With dialog pops up

### Actual Behavior

1. An unhelpful error message appears:


2. Sometimes the mouse pointer disappears, and the "Cancel" button doesn't appear to be keyboard accessible, making it hard to dismiss this dialog.

Start by reproducing the UNC-share file URL behavior in Windows Terminal 1.21.3231.0 using the steps and example in the issue. Trace the URL activation path and Windows file association handling; done means Ctrl+click opens the associated program or Open With dialog without the unhelpful error or an unusable dismissal flow.

Written by the indexing model from the issue text.