Fix compatibility issues with Qt/PyQt6 versions

- Add null check for message.message in search filter
- Handle missing colorScheme/colorSchemeChanged methods for older Qt versions
- Add display check to prevent hanging in headless environments
- Update build documentation with system package alternative
- Update PyInstaller spec for Python 3.12
- Improve run.sh script with venv management

gotify_tray/gui/designs/widget_message.py

@@ -1,6 +1,6 @@
 # Form implementation generated from reading ui file 'gotify_tray/gui/designs/widget_message.ui'
 #
-# Created by: PyQt6 UI code generator 6.9.1
+# Created by: PyQt6 UI code generator 6.10.0
 #
 # WARNING: Any manual changes made to this file will be lost when pyuic6 is
 # run again.  Do not edit this file unless you know what you are doing.