VS Code extension: editing a file-backed API endpoint saves to the wrong path (.universal prefix dropped)

Title: VS Code extension: editing a file-backed API endpoint saves to the wrong path (.universal prefix dropped)

## Summary
In the PowerShell Universal VS Code extension 2026.2.3, using the per-endpoint Edit action on an API endpoint backed by an external script file (-Path) opens and saves the file resolved against the repository root instead of the .universal directory where the runtime actually stores/executes it. Edits are written to the wrong location and never reach the running endpoint — the save silently has no effect.

## Environment
- PowerShell Universal server: 2026.2.3
- VS Code extension: ironmansoftware.powershell-universal 2026.2.3
- Windows; repository at C:\ProgramData\UniversalAutomation\Repository (config-as-code, git-backed)

## Steps to reproduce
1. In the admin UI, create a file-backed endpoint via the Path parameter — URL /pathtest, Path pathtest.ps1. PSU creates ...\Repository\.universal\pathtest.ps1 and stores path = "pathtest.ps1".
2. In VS Code, use the endpoint's Edit action to open pathtest.
3. Modify the code and save.
4. Call GET /api/pathtest.

## Expected
Changes are written to .universal\pathtest.ps1 and, after a configuration reload, the endpoint returns the updated output.

## Actual
- Edit opens/saves a file at the repo root (...\Repository\pathtest.ps1) — a different file from the one the runtime reads.
- The endpoint keeps serving the original code; the edit is silently lost.
- Confirmation: writing directly to .universal\pathtest.ps1 does update the endpoint after reload, proving the runtime file is the .universal copy while Edit targets the repo root.

## Root cause (from the extension code)
- getEditableEndpointPath() returns endpoint.path (e.g. "pathtest.ps1") with no .universal prefix.
- editResource() sets configurationPath = resourcePath for endpoints (unlike scripts, which use getScriptConfigurationPath() with a base folder), then opens createConnectionFileUri(profile, configurationPath).
- The psu:// filesystem provider calls getFileContent(toRelativePath(uri)) -> GET /api/v1/configuration/content/pathtest.ps1, relative to the repo root — not .universal.

The stored path is .universal-relative (runtime), but the extension treats it as repo-root relative (editor); the two resolve to different files.

## Related symptoms
- Inline endpoints (path = null) throw "Endpoint '/api/x' does not have a configuration file path." on Edit.
- A file-backed endpoint whose -Path doesn't match a real file (e.g. -Path "/gam/get_userinfo" when the file is gam/Get_user_info.ps1) is likewise unopenable.

## Impact
Per-endpoint editing of file-backed API endpoints from VS Code does not work — edits appear to succeed but are discarded.

## Suggested fix
Resolve an endpoint's editable path against the .universal directory (the base the runtime uses for -Path), consistent with how scripts resolve via a base folder — e.g. have getEditableEndpointPath()/editResource() prefix .universal/ (or use fullPath) for endpoint resources.