fix: restrict API for pwa to fetch current logged-in employee only (backport #4207)

[mergify]

Summary by CodeRabbit

• Refactor
  • Centralized employee context resolution across attendance, shifts, leave balance, expense claims, and advance features
  • API endpoints now automatically determine the current employee instead of requiring explicit parameters from frontend requests
  • Enhanced consistency and maintainability of employee-scoped data retrieval

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This is an automatic backport of pull request #4207 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1848d34 has failed:

On branch mergify/bp/version-15-hotfix/pr-4207
Your branch is up to date with 'origin/version-15-hotfix'.

You are currently cherry-picking commit 1848d343c.
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	both modified:   hrms/api/__init__.py

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[asmitahase]

This is gonna need manual cherry picking

[frappe-pr-bot]

🎉 This PR is included in version 15.58.3 🎉

The release is available on GitHub release

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