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/__main__.py

@@ -1,11 +1,21 @@
 def main():
+    import os
     import sys
 
     if "--version" in sys.argv:
         from gotify_tray.__version__ import __version__
+
         print(__version__)
     else:
+        # Check for display before importing GUI modules
+        if not os.environ.get("DISPLAY"):
+            print(
+                "Error: No display environment detected. This application requires a graphical desktop environment to run.",
+                file=sys.stderr,
+            )
+            sys.exit(1)
         from gotify_tray.gui import start_gui
+
         start_gui()