add project tooling and test suite for many-rsync

- Add pyproject.toml: hatchling build, many-rsync entrypoint, ruff/mypy/pytest config
with 60% coverage floor
- Add uv.lock for reproducible dev installs
- Add .pre-commit-config.yaml: ruff (with --fix) + mypy hooks
- Add test_main.py: unit tests for _build_rsync_cmd, _load_raw, and load_config
covering happy paths and FATAL exit cases
- Add explanation.md: architecture overview with flowchart
- main.py: refactor into typed, testable functions (_load_raw, _build_rsync_cmd
extracted); add RsyncParameters/Config TypedDicts; add rsync_parameters config support
(rsync_path, exclude_from); harden validation (n clamped, log_level validated)
- README.md: update install instructions and document all config fields including
rsync_parameters

many-rsync/test_main.py

@@ -0,0 +1,105 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from main import _build_rsync_cmd, _load_raw, load_config
+
+# ── _build_rsync_cmd ─────────────────────────────────────────────────────────
+
+
+def test_build_rsync_cmd_no_params() -> None:
+    cmd = _build_rsync_cmd({})
+    assert cmd == ("rsync", "-avh", "--progress", "--delete", "--stats")
+
+
+def test_build_rsync_cmd_with_rsync_path() -> None:
+    cmd = _build_rsync_cmd({"rsync_path": "/usr/local/bin/rsync"})
+    assert "--rsync-path=/usr/local/bin/rsync" in cmd
+
+
+def test_build_rsync_cmd_with_exclude_from() -> None:
+    cmd = _build_rsync_cmd({"exclude_from": ".gitignore"})
+    assert "--exclude-from=.gitignore" in cmd
+
+
+def test_build_rsync_cmd_with_all_params() -> None:
+    cmd = _build_rsync_cmd({"rsync_path": "/opt/rsync", "exclude_from": "exc.txt"})
+    assert "--rsync-path=/opt/rsync" in cmd
+    assert "--exclude-from=exc.txt" in cmd
+
+
+# ── _load_raw ────────────────────────────────────────────────────────────────
+
+
+def test_load_raw_toml(tmp_path: Path) -> None:
+    p = tmp_path / "cfg.toml"
+    p.write_text('remote_folder = "host:/dst"\nlocal_folders = ["a"]\n')
+    raw = _load_raw(p)
+    assert raw["remote_folder"] == "host:/dst"
+
+
+def test_load_raw_json(tmp_path: Path) -> None:
+    p = tmp_path / "cfg.json"
+    p.write_text('{"remote_folder": "/dst", "local_folders": ["a"]}')
+    raw = _load_raw(p)
+    assert raw["remote_folder"] == "/dst"
+
+
+def test_load_raw_unsupported_format(tmp_path: Path) -> None:
+    p = tmp_path / "cfg.yaml"
+    p.write_text("key: val")
+    with pytest.raises(SystemExit):
+        _load_raw(p)
+
+
+# ── load_config ──────────────────────────────────────────────────────────────
+
+
+def test_load_config_valid(tmp_path: Path) -> None:
+    d = tmp_path / "src"
+    d.mkdir()
+    p = tmp_path / "cfg.toml"
+    p.write_text(f'remote_folder = "host:/dst"\nlocal_folders = ["{d}"]\nn = 1\n')
+    cfg = load_config(p)
+    assert cfg["remote_folder"] == "host:/dst"
+    assert cfg["local_folders"] == [d]
+    assert cfg["n"] == 1
+    assert cfg["log_level"] == "INFO"
+
+
+def test_load_config_empty_folders(tmp_path: Path) -> None:
+    p = tmp_path / "cfg.toml"
+    p.write_text('remote_folder = "host:/dst"\nlocal_folders = []\n')
+    with pytest.raises(SystemExit):
+        load_config(p)
+
+
+def test_load_config_missing_remote(tmp_path: Path) -> None:
+    d = tmp_path / "src"
+    d.mkdir()
+    p = tmp_path / "cfg.toml"
+    p.write_text(f'local_folders = ["{d}"]\n')
+    with pytest.raises(SystemExit):
+        load_config(p)
+
+
+def test_load_config_n_clamped(tmp_path: Path) -> None:
+    d = tmp_path / "src"
+    d.mkdir()
+    p = tmp_path / "cfg.toml"
+    p.write_text(f'remote_folder = "host:/dst"\nlocal_folders = ["{d}"]\nn = 99\n')
+    cfg = load_config(p)
+    assert cfg["n"] == 1  # clamped to len(folders)
+
+
+def test_load_config_invalid_log_level(tmp_path: Path) -> None:
+    d = tmp_path / "src"
+    d.mkdir()
+    p = tmp_path / "cfg.toml"
+    p.write_text(
+        f'remote_folder = "host:/dst"\nlocal_folders = ["{d}"]\nlog_level = "TRACE"\n'
+    )
+    with pytest.raises(SystemExit):
+        load_config(p)