b10x init: a single-host plan reports "Nothing to change" while the other host has legacy installs #33

Checked against main at 2f82cbc, b10x 0.14.11.

On a machine with Beyond10x in both Claude Code and Codex, b10x init aep,ess,worktree --host claude reported:

note   codex  codex   Beyond10x plugins are installed for `codex` too and this plan leaves them alone; `--host all` covers both
Nothing to change.

The Codex side was far from current. b10x init … --host codex then planned 10 actions: register the b10x marketplace, install 4 plugins, and remove 5 legacy installs (aep-drive, aep-plan, beyond10x, ess-specify, workspace-hygiene). All 10 ran and converged. The Claude-host plan knew Codex had Beyond10x plugins (crates/b10x/src/plan.rs:351), but not that they were legacy, so "Nothing to change" read as done.

Expected, either of:

1. When another host has Beyond10x installs, the note says what a plan for that host would do: "codex: 5 legacy installs, 4 missing plugins; --host all or --host codex fixes them".
2. b10x init without --host plans for every host that has a Beyond10x install. b10x:init step 4 then passes --host all when both hosts are present.