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

lim/packages.py

@@ -0,0 +1,18 @@
+"""Reads package collections from configuration/packages/."""
+
+from lim import config
+from lim.errors import LimError
+
+
+def get_packages(*collections: str) -> list[str]:
+    """Package names from the given collections, comments stripped."""
+    names: list[str] = []
+    for collection in collections:
+        path = config.PACKAGE_PATH / f"{collection}.txt"
+        if not path.is_file():
+            raise LimError(f"Package collection {path} does not exist.")
+        for line in path.read_text().splitlines():
+            name = line.split("#", 1)[0].strip()
+            if name:
+                names.append(name)
+    return names