Fix f-string syntax errors in fan_widget.py and main_window.py

[kmilodenisglez]

Summary

Fixes a SyntaxError: f-string: unmatched '[' occurring on Python 3.12 and newer versions due to quote reuse within f-string expressions.

Context & Cause

Starting with Python 3.12, the new f-string parser strictly validates quote nesting. Using the same single quote type for both the enclosing f-string and the dictionary key lookup (f'{fan_data['Temperature']:.2f}') throws a syntax error at launch.

Changes Made

• Changed the internal dictionary key lookup single quotes to double quotes ("Temperature") on line 1058 of nbfc-qt.

Testing

• Tested locally on Python 3.12+ / Linux. The application now launches and renders the temperature UI label without throwing a SyntaxError.