feat: add CLI options for custom CSV separator and normalize-to-one branch normalization

beta_spectrum/spectrum.py

@@ -87,6 +87,10 @@ class SpectrumConfig:
     intensity_cutoff: float = (
         0.0  # Ignore branches below this fraction (default: 0.0 = all)
     )
+    
+    # CSV output options
+    csv_separator: str = ','  # Default separator for CSV output
+    normalize_to_one: bool = False  # If True, normalize each branch to 1, ignoring intensity
 
 
 class BetaSpectrum:
@@ -321,6 +325,8 @@ class BetaSpectrum:
 
         # Create per-branch calculators
         branch_spectra: List[BetaSpectrum] = []
+        if config.branches is None:
+            raise ValueError("branches must be provided for multi-branch mode")
         for i, branch in enumerate(config.branches):
             if logger:
                 logger.info(