chore: replace join-path dependency with native path.join

[gameroman]

No description provided.

[gemini-code-assist]

Code Review

This pull request removes the join-path dependency and its associated sub-dependencies from the project, replacing its usage with the native Node.js path module in src/loaders/config-file.js and src/providers/fs.ts. I have no feedback to provide.

[wiz-9635d3485b]

Wiz Scan Summary

Scanner	Findings
Vulnerabilities	-
Sensitive Data	-
Secrets	-
IaC Misconfigurations	-
SAST Findings	1  1
Software Management Findings	-
Total	1  1

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[bkendall]

There was something about this that has worried me in the past - maybe that it didn't work so well on Windows? I'll hopefully take a look at this in the next few days. Thanks!