feat(image): flash full disk images into LUKS; add Raspberry Pi OS

Support distributions that ship a full .img (Raspberry Pi OS, moode, RetroPie,
Manjaro ARM) rather than a rootfs tarball, by loop-mounting the image and
copying its boot + root partitions into a fresh LUKS container.

- distributions.yml/catalog.py/choosers.py: raspios catalog (lite64/desktop64/
  lite32 via the stable _latest redirects) + choose_raspios.
- plan.py: source_url override so a _latest redirect downloads under an .img.xz
  name that decompress_command recognises.
- transfer.py: transfer_disk_image (loop-mount -> repartition -> LUKS -> rsync
  copy with progress, cp fallback -> fix boot fstab); transfer_image gains
  interactive= and routes encrypted non-arch images here; download_image gains
  force_prompt.
- loopimg.py: losetup attach/detach/partition helper.
- fsutil.drop_fstab_mount + register_encrypted_root: replace a stock image's
  existing / fstab line instead of colliding with it.
- encryption.configure_encryption returns the onion address.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lim/fsutil.py

@@ -16,6 +16,23 @@ def replace_in_file(search: str, replace: str, path: str | Path) -> None:
     path.write_text(new_text)
 
 
+def drop_fstab_mount(mount_point: str, path: str | Path) -> None:
+    """Remove any (non-comment) fstab line whose mount point field equals mount_point.
+
+    Lets a fresh mapper/boot entry replace a stock image's existing one instead
+    of colliding with it. No-op when the file or a matching line is absent.
+    """
+    path = Path(path)
+    if not path.exists():
+        return
+    kept = [
+        line
+        for line in path.read_text().splitlines()
+        if line.lstrip().startswith("#") or line.split()[1:2] != [mount_point]
+    ]
+    path.write_text("".join(f"{line}\n" for line in kept))
+
+
 def ensure_line_in_file(line: str, path: str | Path) -> bool:
     """Append ``line`` unless already present. Returns True when appended."""
     path = Path(path)