fix(remote): keep Codeman's pane command away from the remote default-shell

Handing the launch to bash verbatim exposed `"${SHELL:-/bin/sh}"` to the far
end for the first time. tmux runs a one-argument command through the remote
default-shell, not /bin/sh as the comments said, and fish refuses `${...}`:
on a fish host, or a bash login with `set -g default-shell fish`, every new
pane died with status 127. master only survived because the local sh had
already rewritten that token to this host's shell path.

Codeman's own text now goes to `/bin/sh -c` as separate tmux arguments, which
tmux execs without a shell. A commands.* override stays one argument and keeps
the default-shell it was written for: under `/bin/sh` a `source` or `[[` in an
override dies with 127 on bash and zsh hosts.

The tests read the argv tmux would receive through a real sh, so they need no
fish: every stock launch must reach /bin/sh and an override must not. The
docker half of bashCArg was pinned by nothing, so it gets its own test.

Comments that described the removed double-quote layer are corrected, and
remote-hosts.ts no longer claims overrides are seeded from the default text
or that they rescue nushell and elvish.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.changeset/remote-launch-expansion.md

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+---
+"aicodeman": patch
+---
+
+Remote sessions: new sessions no longer die with `tmux: command not found` (exit 127) when the remote user's home differs from the Codeman host's. The launch line reached the local shell in double quotes, so `$HOME` and `$PATH` in the remote PATH bootstrap expanded on the Codeman host before ssh ran. Launches now reach the far end verbatim, which also means a remote session starts in the remote user's own shell rather than the Codeman host's, and a Codeman host whose `$SHELL` path does not exist on the remote no longer kills the pane. Codeman's own pane command now runs through `/bin/sh` so fish hosts keep working, while a per-host `commands.*` override still runs in the remote user's shell. Behaviour change: in a `commands.*` override, `$` now expands on the far end (remote host or container) instead of on the Codeman host, and a bare `$VAR` in a Docker `extraCreateArgs`/`extraExecArgs` value is passed to `docker` literally, so write the value out. Thanks to @Randalix for the report and the fix.