restore Claude Code agents in their own sessions

`dingger install claude` adds a SessionStart hook to Claude's settings
(every other key and hook kept, in order; the original backed up; written
through a symlink; installing again changes nothing). The hook is
`dingger hook claude`: it reports the session's transcript for its tmux
pane, prints nothing (Claude adds SessionStart output to the conversation)
and always exits 0. Claude's state still comes from its screen.

restore types `claude --resume <id>` in the directory the session ran in
(elsewhere, Claude moves the conversation there). it resumes an agent only
when its session file exists: a Claude session that never got a message
has no transcript, and `--resume` fails ("No conversation found"). the
snapshot now keeps an agent's command line too, so such a pane gets it
retyped instead of nothing.

- the hook receiver takes a report without a state: only the session.
- a report that arrives after the watcher listed the panes is not dropped
  as "agent gone": Claude reports once, as it starts.
- serde_json preserve_order (indexmap is already a dependency, via toml).

e2e step 18: install against a settings file like a real one, a fake
claude running the exact installed hook command, resume by id, retype
without a transcript, the resumed agent reporting again. a server that
restore starts now gets the test's plain shells: it got the user's login
shell, whose profile put the real claude first, which started (stuck at
its trust dialog) during development. every test restore now checks that
no real pi or claude runs in a test pane.

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