Unify dataset/tooling scripts into a single dwarf Typer CLI

Replace the five separately-hyphenated uv entry points (steps-to-parquet,
steps-to-parquet-parallel, migrate-geant-steps, bump-dataset-version,
create-root-files) plus the unregistered hparam_scan.py with one `dwarf`
command exposing convert/migrate/bump-gen/bump-schema/status/
update-manifest/create-manifest/make-root/hparam-scan as subcommands.

Each scripts/*.py module now only holds argparse-free business logic;
scripts/dwarf.py wires it up with Typer, matching giant/cli.py's style.
`dwarf convert` merges the old serial/parallel conversion scripts behind
a --jobs flag (default 1: sequential with plain -o; >1: dataset-layout
fan-out via subprocess).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_create_root_files.py

@@ -244,24 +244,3 @@ def test_run_all_caps_concurrency(tmp_path):
         concurrent += delta
         peak = max(peak, concurrent)
     assert peak <= 2
-
-
-def test_build_parser_defaults():
-    args = create_root_files.build_parser().parse_args(
-        [
-            "--executable",
-            "fake",
-            "--detector",
-            "pbwo4",
-            "--num-files",
-            "2",
-            "--events-per-file",
-            "10000",
-            "--gen",
-            "gen1",
-        ]
-    )
-    assert args.jobs == 4
-    assert args.kind == "steps"
-    assert args.dataset_root == "/ceph/lbogner/geant_steps"
-    assert args.execute is False