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/lint/test_file_length.py

@@ -0,0 +1,19 @@
+"""Architecture guard: keep modules small (KISS/SRP)."""
+
+from pathlib import Path
+
+MAX_LINES = 250
+REPO_ROOT = Path(__file__).resolve().parents[2]
+CHECKED_GLOBS = ("main.py", "lim/**/*.py", "tests/**/*.py")
+
+
+def test_source_files_stay_below_max_lines():
+    offenders = {
+        str(path.relative_to(REPO_ROOT)): length
+        for pattern in CHECKED_GLOBS
+        for path in sorted(REPO_ROOT.glob(pattern))
+        if (length := len(path.read_text().splitlines())) > MAX_LINES
+    }
+    assert not offenders, (
+        f"Files exceeding {MAX_LINES} lines (split them, see KISS/SRP): {offenders}"
+    )