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/image/plan.py

@@ -0,0 +1,31 @@
+"""The image setup plan collected from the user's answers."""
+
+from dataclasses import dataclass, field
+from pathlib import Path
+
+DEFAULT_BOOT_SIZE = "+500M"
+
+
+@dataclass
+class ImagePlan:
+    operation_system: str = "linux"
+    distribution: str | None = None
+    base_download_url: str | None = None
+    image_name: str | None = None
+    image_checksum: str | None = None
+    boot_size: str = ""
+    luks_memory_cost: str | None = None
+    raspberry_pi_version: str | None = None
+    encrypt_system: bool = False
+    root_filesystem: str = ""
+    image_folder: Path = field(default_factory=Path)
+
+    @property
+    def download_url(self) -> str | None:
+        if self.base_download_url is None or self.image_name is None:
+            return None
+        return f"{self.base_download_url}{self.image_name}"
+
+    @property
+    def image_path(self) -> Path:
+        return self.image_folder / self.image_name