feat: add lexists template function

[JamBalaya56562]

Summary

Adds a lexists template function — the os.Lstat counterpart of the existing exists.

exists is backed by os.Stat, which follows symlinks, so a symlink whose target is missing (a dangling link) reports as non-existent. lexists uses os.Lstat, which stats the link itself without following it, so it returns true for the symlink even when its target is unavailable. This is the behaviour requested in #187 (check for existence without traversing the symlink).

Change

• internal/utils: add PathLExists, mirroring PathExists but using os.Lstat instead of os.Stat (same fs.ErrNotExist handling).
• internal/template: register it in the template FuncMap as lexists, next to exists.
• README.md: document lexists alongside exists.

Tests

TestPathLExists covers an existing file (true), a missing path (false), and — the distinguishing case — a dangling symlink, asserting lexists returns true while exists returns false. The symlink portion is skipped where symlink creation isn't permitted (e.g. Windows without the privilege).

Fixes #187

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