Add Windows installer and migrate inference to ONNX Runtime

[JosephDriedger]

Summary

• Replaced TensorFlow/Keras inference with ONNX Runtime to resolve DLL
  loading failures in the PyInstaller build on Windows
• Converted spectrogram_classifier.h5 to spectrogram_classifier.onnx
• Added PyInstaller build with a runtime hook (hook_runtime.py) to
  register native DLL directories before onnxruntime loads
• Fixed resource paths to resolve correctly from both source and the
  bundled executable (sys._MEIPASS)
• Added Inno Setup script (installer.iss) to produce a Windows installer
• Updated .gitignore, requirements.txt, and README with new build instructions

Test plan

• Run python gui.py from source and confirm songs load and detection works
• Build with PyInstaller command from README and confirm exe launches
• Compile installer.iss with Inno Setup and run MelodiProof-AI-Setup.exe
• Verify Play/Stop and Run Detection work in the installed build