Implement missing Spectrogram node for AudioProcess pipeline

[Copilot]

The Spectrogram node was registered in the UI menu but lacked the required FactoryNode implementation, making it non-functional.

Implementation

Added node/AudioProcessNode/node_spectrogram_node.py:

• FactoryNode class defining UI with AUDIO input, IMAGE output, configurable FFT size and colormap
• SpectrogramNode class implementing audio→spectrogram pipeline using existing utility functions (fourier_transformation, make_logscale)
• Matplotlib compatibility fix: buffer_rgba() replaces deprecated tostring_rgb()

Added test coverage:

• Basic instantiation and attribute validation
• Integration tests with synthetic audio (440Hz sine wave)
• Verification across FFT sizes (512/1024/2048/4096) and colormaps (jet/viridis/plasma/inferno/magma/hot/cool)

Added documentation (EN/FR):

• Usage guide and technical specifications
• Audio format: {'samples': np.ndarray, 'sample_rate': int}
• Output: BGR image compatible with OpenCV pipeline

Usage

# In CV_Studio node editor:
# AudioProcess → Spectrogram
# Connect: Video[Audio Output] → Spectrogram[Audio Input]
# Configure: FFT=1024, Colormap=jet
# Output: Spectrogram[Image Output] → downstream nodes

No existing files modified. All changes additive.

Original prompt

je n'arrive pas de faire fonctionnement le noed spectrogramme

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