Retaining link-in-place behind a prompt and DSH_ADOPT kept the divergent
install shape that this change exists to remove, and cost a flag, a prompt,
a dirty-tree warning, a no-commit fallback, and a second linking path.
In-repo mode now adopts unconditionally. A dirty tree adopts silently:
`worktree add` from HEAD cannot carry uncommitted work, so a prompt only
adds a decision the user cannot act on differently.
The original reason for link-in-place — keeping the script testable against
local source — survives adoption, since the staging worktree branches from
the checkout's HEAD and runs the same code. DSH_SOURCE remains the escape
hatch for installing a separate tree.
Net 47 fewer lines in the installer.
00c5f2abd1