Copilot ghost text (inline suggestions) does not work for source members opened via the "member:" scheme

**Is your feature request related to a problem? Please describe.**
When editing a source member opened through Code for IBM i (a document with the "member:" URI scheme), GitHub Copilot's inline suggestions (ghost text) never appear, even though the same content in a local file works fine. Language mode and editability are identical between the two, and the Copilot status bar icon shows no warning. The GitHub Copilot Chat Output panel shows zero log activity for member: documents but normal activity for local files — indicating Copilot's inline completion provider silently filters out this custom scheme before ever attempting a request. I've filed the underlying request with the VS Code/Copilot team here: https://github.com/microsoft/vscode/issues/335774

**Describe the solution you'd like**
Ideally this gets resolved upstream in Copilot's inline completion provider (see linked issue). From Code for IBM i's side, it would help to track this as a known limitation, and potentially investigate whether exposing member content differently (e.g. a scheme Copilot already supports) could work around it.

**Describe alternatives you've considered**
Downloading/editing a local copy of the member and deploying it back gets ghost text, but loses the direct virtual-member editing workflow.

**Additional context**
Confirmed with editor.inlineSuggest.enabled set to true, on Code for IBM i 3.0.13.

Start with the linked VS Code/Copilot issue and reproduce the behavior using an editable member: document in Code for IBM i 3.0.13, with editor.inlineSuggest.enabled set to true. Compare Copilot Chat Output activity for member: and local files, then investigate whether a supported document scheme can preserve the virtual-member workflow. Done means an upstream fix, a confirmed viable workaround, or clear documentation of the limitation.

Written by the indexing model from the issue text.