refactor: rename visualize module to output module and separate concerns into core, csv_export, and visualization modules

beta_spectrum/output/__init__.py

@@ -0,0 +1,23 @@
+"""
+Output module — BetaSpectrumAnalyzer class and related functionality.
+
+Introspection, analysis, visualization and export tools for BetaSpectrum.
+All nuclides (single- and multi-branch) are treated uniformly as one or more
+branches — single-branch is just a special case with one branch.
+"""
+
+from __future__ import annotations
+
+from .core import BetaSpectrumAnalyzer, _UnifiedBranch
+from .csv_export import CSVEmitter
+from .visualization import Visualizer
+
+# Re-export the main class for backward compatibility
+BetaSpectrumAnalyzer = BetaSpectrumAnalyzer
+
+__all__ = [
+    "BetaSpectrumAnalyzer",
+    "CSVEmitter",
+    "Visualizer",
+    "_UnifiedBranch",
+]