fix: disclose the tcsh regression and bring the launch docs in line (release review)

A tcsh login shell worked on 1.48.0 only because the local sh rewrote
${SHELL:-/bin/sh} to this host's shell. With the launch verbatim, tcsh gets -i -l,
refuses it and every stock launch leaves a dead pane. The changeset and
docs/remote-sessions.md described that as a standing limitation; they now name it
as a change in this release, with what the override workaround costs.

Also: extraSshOptions joins the list of values now literal at launch, the stock pane
command is shown as /bin/sh -c in the docs and the builder's JSDoc, the invariants
state how the launch must reach the far end, the manual pages cover $ in an override,
and the invariants no longer say extraSshOptions refuses a bare $ (it never did).

Reworded the em-dashes on the invariants line this rewrites.

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

src/tmux-manager.ts

@@ -1284,12 +1284,15 @@ export function remoteTmuxLocation(remote: SessionRemote, sessionId: string): {
  *
  * Emits:
  *   ssh -o BatchMode=yes -t [<COD-107 connection opts>] user@host \
- *     'tmux -L codeman-remote new-session -A -s codeman-ssh-<id> -c <path> "cd <path> && exec <cli>" \
+ *     'tmux -L codeman-remote new-session -A -s codeman-ssh-<id> -c <path> /bin/sh -c <pane-command> \
  *        \; set -t codeman-ssh-<id> status off \; set -t codeman-ssh-<id> mouse off \
  *        \; set -t codeman-ssh-<id> prefix C-q \; set -s escape-time 0 \; \
  *        bind-key -T prefix C-q send-prefix \; unbind-key -a -T prefix \; \
  *        bind-key -T prefix C-q send-prefix \; set -t codeman-ssh-<id> remain-on-exit failed'
  *
+ * `<pane-command>` is `cd <path> && exec <cli>`, quoted as one token. A per-host `commands.*`
+ * override is that one token alone, with no `/bin/sh -c` in front of it.
+ *
  * COD-107 — the connection options (`-p`, `-i`, `-J`, SOCKS `-o ProxyCommand`,
  * arbitrary `-o`) come from the shared `buildSshConnectionArgs(remote)`, so the
  * prereq tmux probe and this launch connect with identical options.