Arch Vulkan Dependency Check Fix

This maintenance release improves dependency detection for the llama.cpp Manager, with a focus on Arch Linux and the Vulkan backend.

What’s New:

• Arch Vulkan Headers: Added the required vulkan-headers package to the pacman Vulkan dependency list alongside vulkan-devel, shaderc, and spirv-headers.
• Real Package Checks: The manager now checks installed packages through pacman, dpkg, or rpm instead of considering only compiler/tool binaries.
• Missing Package UI: Missing packages are shown in the dependency panel, and Install Missing remains enabled until all required packages are installed.
• Validation: After dependency installation, the status is refreshed so the button is disabled only when the selected backend is actually ready.