Live Preview omits initial slash of URL pathname if `livePreview.openPreviewTarget` is "External Browser" and `livePreview.serverRoot` ends with a slash.

• Live Preview version: 0.4.15
• VS Code version: 1.101.1
• OS version: macOS 15.5

Steps to Reproduce:

1. Create or open a workspace.
2. Create a folder in the workspace root such as "public".
3. In the workspace settings, set livePreview.serverRoot to that folder's path with a trailing slash (e.g. "/public/").
4. In the workspace or user settings, set livePreview.openPreviewTarget to "External Browser".
5. Create or open an HTML file in the folder from step 2 such as /public/index.html.
6. Open a preview of that file.

Expected result: VS Code tells the default browser to open http://127.0.0.1:3000/index.html.

Actual result: VS Code tells the default browser to open http://127.0.0.1:3000index.html/.
(See screenshot. Note the missing slash between port and filename, and the appended trailing slash.)

Start by tracing the URL construction used when livePreview.openPreviewTarget is "External Browser", reproducing the case with livePreview.serverRoot set to "/public/" and an index.html file. Done means the external browser receives http://127.0.0.1:3000/index.html, with neither the missing slash nor the appended trailing slash.