Provisioning was still installing `claude` and `pi` through a separate
npm-global prefix even after the guest images had switched to `mise` for
Node and opencode. That left two competing install paths and made the
runtime layout harder to reason about.
Switch the Debian and Void image setup flows to install `claude` and `pi`
as `mise` npm tools, assert their shims exist after `mise reshim`, and
symlink `node`, `npm`, `opencode`, `claude`, and `pi` directly from the
mise shim directory into `/usr/local/bin`.
Update the imagebuild test expectations and bump the Void rootfs default
size to 4G so the larger default toolset still fits reliably.