Remove repeated per-branch metadata columns from CSV export

Branch intensity, endpoint, and transition are constant per branch and
already documented in the CSV header. No need to repeat them as columns
for every energy row.

beta_spectrum/spectrum.py

@@ -1572,19 +1572,9 @@ class BetaSpectrumAnalyzer:
 
         if self._is_multi and self.spectrum.branches:
             # Multi-branch mode: total spectrum + per-branch spectra + components
-            for i, (branch, branch_spec) in enumerate(
-                zip(self.spectrum.branches, self.spectrum.branch_spectra)
-            ):
+            # (branch info — intensity, endpoint, transition — is in the header, not repeated columns)
+            for i, branch_spec in enumerate(self.spectrum.branch_spectra):
                 data[f"branch_{i+1}_spectrum"] = branch_spec(self.W)
-                data[f"branch_{i+1}_intensity"] = np.full_like(
-                    self.energies_MeV, branch.intensity
-                )
-                data[f"branch_{i+1}_endpoint"] = np.full_like(
-                    self.energies_MeV, branch.endpoint_MeV
-                )
-                data[f"branch_{i+1}_transition"] = np.full_like(
-                    self.energies_MeV, branch.transition_type, dtype=object
-                )
 
             # Per-branch components (PhaseSpace, Radiative, etc.)
             for i, branch_spec in enumerate(self.spectrum.branch_spectra):