fix(loader): restore legacy slash-prefixed class resolution for container:graph

[Copilot]

Service configs using slash-prefixed class references (e.g. class: /Kernel) cause container:graph to throw Cannot find module '/Kernel' because /Kernel is treated as an absolute filesystem path rather than a relative module name.

Root cause

In FileLoader._requireClassNameFromPath, path.isAbsolute('/Kernel') returns true, so _getFromDirectoryByClassObject sets fromDirectory = '/'. This makes path.join('/', '/Kernel') = '/Kernel', causing require('/Kernel') to fail as a bare absolute path with no corresponding file.

Changes

• lib/Loader/FileLoader.js — Normalize single-segment slash-prefixed class names at the entry of _requireClassNameFromPath before resolution:

  // '/Kernel' → 'Kernel'; multi-segment absolute paths like '/home/user/Kernel.js' are untouched
  const normalizedClass = (classObject && classObject.startsWith('/') && classObject.lastIndexOf('/') === 0)
    ? classObject.slice(1)
    : classObject

  After normalization Kernel resolves correctly relative to the config file's directory. Real absolute paths (multiple segments) are unaffected.

• test/Resources/config/slash-prefixed-class.yml + test/Resources/config/Kernel.js — Test fixtures for the legacy pattern.

• test/node-dependency-injection/lib/Loader/YamlFileLoader.spec.js — Regression test: load, compile, and resolve a service defined with class: /Kernel.