Add initial version of the Axira Zsh theme.
Features:

• VPN IP detection with fallback to eth0
• Smart icon: 🔒 for VPN, 🌐 when not connected
• Python venv and Git branch shown
• Clean multi-line style with Nerd Font symbols

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

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Other comments:

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