fix(enclave): support bare strings in mounts config

[mgabor3141]

Mounts can now be bare strings for the common read-write case:

mounts = ["~/dev/myproject/.jj", "~/dev/myproject/.git"]

Object form still works for read-only mounts:

mounts = [
  "~/dev/myproject/.jj",
  { path = "~/shared/configs", readonly = true },
]

Also fixes ASCII chart alignment in README.