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.spec

@@ -8,7 +8,7 @@ logo = "gotify_tray/gui/images/logo.ico" if platform.system() != "Darwin" else "
 
 a = Analysis(['gotify_tray/__main__.py'],
              pathex=[os.getcwd()],
-             binaries=[('/lib/x86_64-linux-gnu/libpython3.10.so', '.'), ('/lib/x86_64-linux-gnu/libpython3.10.so.1', '.')],
+              binaries=[('/lib/x86_64-linux-gnu/libpython3.12.so', '.'), ('/lib/x86_64-linux-gnu/libpython3.12.so.1', '.')],
              datas=[('gotify_tray/gui/images', 'gotify_tray/gui/images'), ('gotify_tray/gui/themes', 'gotify_tray/gui/themes')],
              hiddenimports=[],
              hookspath=[],