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/integration/test_cli_flows.py

@@ -66,12 +66,12 @@ def n_points_of(header: List[str]) -> int:
 class TestCLIJsonFlows:
     """Options must propagate through the JSON config flow (D2)."""
 
-    def test_json_honors_normalize_to_one_and_tab_separator(
+    def test_json_honors_separate_branches_and_tab_separator(
         self, tmp_path: Any
     ) -> None:
         src = write_json(tmp_path)
         out = str(tmp_path / "to_one.csv")
-        main([src, "--output", out, "--normalize-to-one", "--csv-separator", "tab"])
+        main([src, "--output", out, "--separate-branches", "--csv-separator", "tab"])
 
         with open(out) as f:
             body = "".join(ln for ln in f if not ln.startswith("#"))
@@ -136,7 +136,7 @@ class TestCLIDegenerateFlows:
                     out,
                     "--neutrino-mass",
                     "0.35",
-                    "--normalize-to-one",
+                    "--separate-branches",
                 ]
             )
         assert exc.value.code == 1
@@ -147,9 +147,9 @@ class TestCLIDegenerateFlows:
 class TestCLIPaceENSDF:
     """paceENSDF flow honors the same export options."""
 
-    def test_paceensdf_honors_normalize_to_one(self, tmp_path: Any) -> None:
+    def test_paceensdf_honors_separate_branches(self, tmp_path: Any) -> None:
         out = str(tmp_path / "p32.csv")
-        main(["P32", "--output", out, "--normalize-to-one"])
+        main(["P32", "--output", out, "--separate-branches"])
 
         df = read_export(out)
         assert "total_spectrum" not in df.columns