refactor!: port shell scripts to Python package

Bash scripts were untestable and duplicated device/LUKS/mount logic;
the lim/ package centralizes it behind one subprocess wrapper and a
YAML image catalog (single point of truth).

BREAKING CHANGE: scripts/*.sh removed. Use `lim --type <cmd>`; new
types mount/umount/single-boot/raid1-boot/lock/unlock/import/export
replace direct script calls. --extra is deprecated and ignored.

- distributions.yml + lim/catalog.py hold the image catalog (PyYAML)
- pytest suite: 102 tests with mocked subprocess (tests/unit) and a
  250-line max file-length guard (tests/lint)
- ruff strict (select ALL), GitHub Actions CI, Dependabot; Travis gone
- Makefile: install (symlink ~/.local/bin/lim) and test targets
- fixes over bash: SUDO_USER-aware chown, mmcblk/nvme partition paths,
  sha512 checksum support, whole-pipeline failure detection, blkid
  UUID fallback for pre-mounted images, conditional fstab seeding for
  PARTUUID/LABEL images, clean errors for missing binaries

tests/unit/test_packages.py

@@ -0,0 +1,30 @@
+import pytest
+
+from lim import config, packages
+from lim.errors import LimError
+
+
+@pytest.fixture
+def package_dir(tmp_path, monkeypatch):
+    monkeypatch.setattr(config, "PACKAGE_PATH", tmp_path)
+    return tmp_path
+
+
+def test_strips_comments_and_blank_lines(package_dir):
+    (package_dir / "general.txt").write_text(
+        "# header comment\nnano\ntree# inline comment\n\nhtop\n"
+    )
+    assert packages.get_packages("general") == ["nano", "tree", "htop"]
+
+
+def test_multiple_collections_are_concatenated(package_dir):
+    (package_dir / "a.txt").write_text("one\n")
+    subdir = package_dir / "server"
+    subdir.mkdir()
+    (subdir / "luks.txt").write_text("two\nthree\n")
+    assert packages.get_packages("a", "server/luks") == ["one", "two", "three"]
+
+
+def test_missing_collection_raises(package_dir):
+    with pytest.raises(LimError):
+        packages.get_packages("does-not-exist")