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)

tests/quality/test_cli_options.py

@@ -0,0 +1,137 @@
+"""CLI option surface tests: renamed branch-separation flag, short
+aliases for every long option, and dry-run output shape (audit follow-up
+by the maintainer: rename --normalize-to-one, add short options, drop the
+redundant top-level Transition line)."""
+
+from __future__ import annotations
+
+import dataclasses
+from typing import Any, Optional
+
+import pytest
+
+from beta_spectrum import BranchConfig, SpectrumConfig
+from beta_spectrum.cli import _build_parser, _print_dry_run_output
+
+pytestmark = pytest.mark.quality
+
+
+def make_config() -> SpectrumConfig:
+    return SpectrumConfig(
+        Z_parent=59,
+        Z_daughter=60,
+        A_number=144,
+        endpoint_MeV=2.98,
+        transition_type="F1",
+        e_step_MeV=0.001,
+        branches=[
+            BranchConfig(endpoint_MeV=2.98, transition_type="F1", intensity=0.9),
+            BranchConfig(endpoint_MeV=2.1, transition_type="A", intensity=0.1),
+        ],
+    )
+
+
+class TestSeparateBranchesRename:
+    """--normalize-to-one was renamed to --separate-branches (no alias)."""
+
+    def test_flag_parses_true(self) -> None:
+        parser = _build_parser()
+        args = parser.parse_args(["input.json", "--separate-branches"])
+        assert args.separate_branches is True
+
+    def test_flag_default_is_none(self) -> None:
+        parser = _build_parser()
+        args = parser.parse_args(["input.json"])
+        assert args.separate_branches is None
+
+    def test_old_flag_is_rejected(self) -> None:
+        parser = _build_parser()
+        with pytest.raises(SystemExit):
+            parser.parse_args(["input.json", "--normalize-to-one"])
+
+    def test_config_field_renamed(self) -> None:
+        names = {f.name for f in dataclasses.fields(SpectrumConfig)}
+        assert "separate_branches" in names
+        assert "normalize_to_one" not in names
+
+    def test_config_old_kwarg_rejected(self) -> None:
+        kwargs: dict[str, Any] = {
+            "Z_parent": 15,
+            "Z_daughter": 16,
+            "A_number": 32,
+            "endpoint_MeV": 1.7103,
+            "transition_type": "A",
+            "normalize_to_one": True,
+        }
+        with pytest.raises(TypeError):
+            SpectrumConfig(**kwargs)
+
+
+# (short, long, value-or-None-for-store_true)
+_SHORT_EQUIV = [
+    ("-N", "--nuclide", "Cs137"),
+    ("-i", "--input", "in.json"),
+    ("-s", "--e-step", "0.01"),
+    ("-m", "--neutrino-mass", "0.15"),
+    ("-o", "--output", "out.csv"),
+    ("-p", "--plot", "plot.png"),
+    ("-L", "--log-file", "calc.log"),
+    ("-d", "--dry-run", None),
+    ("-c", "--intensity-cutoff", "0.5"),
+    ("-V", "--csv-verbosity", "concise"),
+    ("-S", "--csv-separator", "tab"),
+    ("-b", "--separate-branches", None),
+]
+
+
+class TestShortOptions:
+    """Every long option gains a single-letter alias (only -v/-q existed)."""
+
+    @pytest.mark.parametrize(
+        "short,long,value",
+        _SHORT_EQUIV,
+        ids=[s.lstrip("-") for s, _, _ in _SHORT_EQUIV],
+    )
+    def test_short_matches_long(
+        self, short: str, long: str, value: Optional[str]
+    ) -> None:
+        parser = _build_parser()
+        argv_long = [long] if value is None else [long, value]
+        argv_short = [short] if value is None else [short, value]
+        args_long = parser.parse_args(["Tc99"] + argv_long)
+        args_short = parser.parse_args(["Tc99"] + argv_short)
+        dest = long.lstrip("-").replace("-", "_")
+        assert getattr(args_short, dest) == getattr(args_long, dest)
+        assert getattr(args_long, dest) is not None or value is None
+
+    def test_existing_shorts_unchanged(self) -> None:
+        parser = _build_parser()
+        args = parser.parse_args(["Tc99", "-v", "-q"])
+        assert args.verbose == 1
+        assert args.quiet is True
+
+
+class TestDryRunOutputShape:
+    """The top-level Transition line is redundant with the per-branch
+    list (for multi-branch runs) and was removed."""
+
+    def test_multi_branch_dry_run_no_top_level_transition(self, capsys: Any) -> None:
+        _print_dry_run_output(make_config(), "paceENSDF")
+        out = capsys.readouterr().out
+        assert "Transition:" not in out
+        assert "transition=F1" in out
+        assert "transition=A" in out
+        assert "Multi-branch mode: 2 branches" in out
+
+    def test_single_branch_dry_run_reports_endpoint(self, capsys: Any) -> None:
+        config = SpectrumConfig(
+            Z_parent=15,
+            Z_daughter=16,
+            A_number=32,
+            endpoint_MeV=1.7103,
+            transition_type="A",
+        )
+        _print_dry_run_output(config, "json")
+        out = capsys.readouterr().out
+        assert "Transition:" not in out
+        assert "Mode: single-branch" in out