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

[ba2hannn]

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.

[ba2hannn]

Update: I've also submitted PR #551 which adds an I/O Devices sensor that lists connected USB devices. While this doesn't directly fix the "No Data" message for fans on systems without hwmon fan sensors, it adds useful peripheral device monitoring. The fan "No Data" issue on systems like TUXEDO laptops (where fan data is only available via tuxedo-io kernel module) would require a separate D-Bus integration effort.