feat(cli): separate-branches rename, short aliases, clean dry-run

- --normalize-to-one renamed to --separate-branches (no alias; the
  name now describes the output choice: total spectrum with
  intensity-normalized branches vs separate branches, each
  normalized to unit area with intensities left to the data user).
  SpectrumConfig.normalize_to_one -> separate_branches, CSV header
  word to_one -> separate.
- every long option gains a single-letter alias: -N -i -s -m -o -p
  -L -d -c -V -S -b (only -v/-q existed before)
- dry-run drops the top-level Transition: line — the per-branch
  list below already reports each branch's transition type
- version bumped to 0.4.1 (pyproject, __version__, CSV semantics
  docstring, TODO roadmap entry)

beta_spectrum/nuclear_data.py

@@ -477,7 +477,7 @@ def decay_info_to_config(
     intensity_cutoff: float = 0.0,
     neutrino_mass_MeV: float = 0.0,
     csv_separator: str = ",",
-    normalize_to_one: bool = False,
+    separate_branches: bool = False,
 ) -> SpectrumConfig:
     """
     Convert DecayInfo to a SpectrumConfig.
@@ -494,8 +494,9 @@ def decay_info_to_config(
         Neutrino mass in MeV.
     csv_separator : str
         CSV column separator.
-    normalize_to_one : bool
-        If True, normalize each branch to 1, ignoring intensity.
+    separate_branches : bool
+        If True, emit separate branch spectra, each normalized to
+        integrate to 1 (intensity ignored; no total spectrum column).
 
     Returns
     -------
@@ -535,7 +536,7 @@ def decay_info_to_config(
         branches=branches,
         intensity_cutoff=intensity_cutoff,
         csv_separator=csv_separator,
-        normalize_to_one=normalize_to_one,
+        separate_branches=separate_branches,
     )
 
 
@@ -708,7 +709,7 @@ def create_config_from_source(
         intensity_cutoff = kwargs.get("intensity_cutoff", 0.0)
         neutrino_mass = kwargs.get("neutrino_mass_MeV", 0.0)
         csv_separator = kwargs.get("csv_separator", ",")
-        normalize_to_one = kwargs.get("normalize_to_one", False)
+        separate_branches = kwargs.get("separate_branches", False)
         info = get_decay_info_from_paceENSDF(nuclide, decay_type, decay_index)
         return decay_info_to_config(
             info,
@@ -716,7 +717,7 @@ def create_config_from_source(
             intensity_cutoff=intensity_cutoff,
             neutrino_mass_MeV=neutrino_mass,
             csv_separator=csv_separator,
-            normalize_to_one=normalize_to_one,
+            separate_branches=separate_branches,
         )
     elif source == "json":
         if not json_path: