Feature: Show 'No fan sensors detected' message instead of hiding fan section entirely #548

Has this issue been covered in the Wiki?

• I have read the Wiki and my issue is not covered.

Is there an existing issue reported already?

• I have searched the existing issues, it does not exist.

Describe the problem

On some laptops (including mine), the kernel does not expose any fan sensors through hwmon. In this case:

• sensors command shows no fan entries
• /sys/class/hwmon/ has no fan*_input files
• The Vitals extension shows an empty Fan section with just "No Data"

Expected behavior

It would be helpful if Vitals could:

1. Show a more descriptive message like "No fan sensors detected on this system" instead of just "No Data"
2. Optionally auto-hide the fan section when no fan sensors are detected, to avoid cluttering the menu

System info

• Distribution: Ubuntu 24.04
• Kernel: 6.8.0-117-generic
• GNOME: 46
• Vitals: 75
• sensors output: Shows coretemp, nvme, BAT0, iwlwifi, acpitz - but no fan entries
• /sys/class/hwmon/ fan files: None found

This is related to #547 but is a separate UX issue about how the extension handles the complete absence of fan sensors.