fix: handle non-file URI schemes gracefully in shellcheck linting

[taronsung]

Summary

Fix for linting error when opening files via virtual filesystems (WebDAV, kio-fuse, etc.).

Closes #1370

Problem

When using editors like Kate on KDE Plasma with WebDAV-mounted files, the document URI uses a non-file: scheme (e.g., kio-fuse://...). The linter would throw:

TypeError [ERR_INVALID_URL_SCHEME]: The URL must be of scheme file

This occurred because fileURLToPath() from Node.js only accepts file: URIs.

Solution

Added a safeFileURLToPath helper function that:

1. Checks if the URI uses the file: protocol
2. Returns the file path for valid file: URIs
3. Returns null for non-file: URIs or invalid URIs

When the document path cannot be determined, linting proceeds without adding the document's directory to the source paths. This means ShellCheck's --source-path will only include explicitly configured paths, but linting will still work for the document content itself.

Testing

Added a test case to verify that non-file: URI schemes are handled gracefully without throwing errors.

Notes

• Linting still works for non-file: URIs - it just won't include the document's directory in the source search path
• Users with such setups can explicitly configure sourcePaths in their LSP client settings if needed

[skovhus]

Thanks, can you just run pnpm lint to apply formatting?

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.59%. Comparing base (13a26c2) to head (84ec668).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
server/src/shellcheck/index.ts	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1371      +/-   ##
==========================================
+ Coverage   80.55%   80.59%   +0.03%     
==========================================
  Files          29       29              
  Lines        1502     1510       +8     
  Branches      371      373       +2     
==========================================
+ Hits         1210     1217       +7     
- Misses        234      235       +1     
  Partials       58       58              

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