feat(icons): Use universal code tag icon (nf-fa-code) for 'Dev' directory.

[aelodev]

This Pull Request introduces a dedicated, universally representative icon for the Dev directory.

Motivation:

1. High Usage, Non-Standard Nature: The Dev directory is extremely common within the developer community as the default place for all project repositories and code workspaces. However, it is not a standard, system-level directory (like Documents or Pictures). Since it serves a critical, general-purpose function for users running eza, it should have its own distinct visual glyph.
2. Clarity and Neutrality: Previous options for a generic code folder (like icons tied to Git, NPM, or specific languages) are too opinionated. This new mapping uses the universal code tag icon (nf-fa-code, or \u{f121}) to clearly represent "code" and "development" (</>) without suggesting a dependency on any specific tool or language.

Change:
The directory name Dev is now mapped to the universal code tag icon, providing immediate visual context for a user's primary code workspace.