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/spectrum.py

@@ -57,9 +57,6 @@ class SpectrumConfig:
     """
     Configuration for beta spectrum calculation.
 
-    Supports declarative detector response specification:
-    to enable automatic detector smearing via convolve_with_detector().
-
     Supports multi-branch decay via the `branches` field. When branches are
     provided, the total spectrum is the intensity-weighted sum of individual
     branch spectra. Each branch has its own endpoint energy and transition type.
@@ -90,9 +87,10 @@ class SpectrumConfig:
 
     # 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
+    separate_branches: bool = (
+        False  # If True: emit separate branch spectra, each normalized to
     )
+    # integrate to 1 (intensity ignored); no total spectrum column
 
 
 def _effective_single_fields(config: SpectrumConfig) -> Tuple[float, str]: