docs: update documentation files and fix linting issues

README.md

@@ -62,8 +62,11 @@ beta_shape_pnpi/
 │       │   ├── exchange.py              ✓ Hayen-2018 empirical fit coefficients
 │       │   ├── radiative.py             ✓ Outer radiative corrections, soft-photon resummation
 │       │   └── detector_response.py     ✓ Analytical detector response models
-├── beta_spectrum/visualize/ ← plotting / visualization
-│   └── __init__.py          # BetaSpectrumAnalyzer
+├── beta_spectrum/output/    ← output, plotting, visualization, CSV export
+│   ├── __init__.py          # BetaSpectrumAnalyzer, CSVEmitter, Visualizer
+│   ├── core.py              # BetaSpectrumAnalyzer base class
+│   ├── csv_export.py        # CSV export functionality
+│   └── visualization.py     # Plotting and visualization functionality
 ├── exp_data/                ← experimental data handling
 │   ├── __init__.py          # ExpSpectrum, EnergyCalibrator, GaussianFitter, etc.
 │   ├── spectrum.py          # ExpSpectrum dataclass (energies, counts, errors, metadata)
@@ -117,7 +120,7 @@ Defined in `beta_spectrum/spectrum.py`. Orchestrates the calculation:
 
 ### `BetaSpectrumAnalyzer`
 
-In `beta_spectrum.visualize`. Provides debugging and visualization tools:
+In `beta_spectrum.output`. Provides debugging and visualization tools:
 
 - `total_spectrum(normalize=True/False)` — computed spectrum array
 - `plot_analysis(save_path=None, show_components=True)` — plot with two modes:
@@ -133,7 +136,7 @@ ______________________________________________________________________
 
 ```python
 from beta_spectrum import SpectrumConfig, BetaSpectrum
-from beta_spectrum.visualize import BetaSpectrumAnalyzer
+from beta_spectrum.output import BetaSpectrumAnalyzer
 
 config = SpectrumConfig(
     Z_parent=90,       # Thorium-232 (example)