Fix Windows runtime bundle paths

[denusklo]

Summary

Fixes #651.

• Normalize logical libphp file-map keys before CGI/FPM exclusions and executable-mode assignments.
• Use POSIX keys for harvested user files too, while preserving physical filesystem paths.
• Add regression coverage for native, slash, backslash and mixed input keys, file modes, exclusions, PHP ini merging, and real fixture packaging.
• Make existing path/CGI test expectations portable and isolate environment changes between tests.

Verification

Tested commit 1ccf132 independently on Windows x64, Ubuntu WSL2 x64 and macOS arm64. On each host:

• npm run build passes.
• Full Jest suite passes.
• Real installed runtime files are collected with POSIX keys, intact physical paths, executable PHP/Composer modes and CGI/FPM exclusions.

Node versions: Windows 22.19.0, WSL2 22.23.2, macOS 22.23.3. No Vercel deployment was performed; these checks validate build-time packaging.

Related work

This is independent of #642. That PR fixes local Composer execution, while this failure happens earlier during runtime file collection. No Composer execution behavior changes here.