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>

src/web/schemas.ts

@@ -878,11 +878,11 @@ const RemoteCommandOverridesSchema = z
 const NO_SHELL_INJECTION = /^[^\n\r\0`]*$/;
 const noCommandSubstitution = (s: string) => !s.includes('$(');
 
-// `remotePath`/`identityFile` are shell-escaped, then the whole launch command is
-// embedded via `JSON.stringify(...)` inside `bash -c "..."` (tmux-manager). That
-// outer DOUBLE-quote layer re-exposes `$(...)`, backticks, and `$VAR` even though
-// the inner value is single-quoted — so a `$(cmd)` in the path would run LOCALLY at
-// launch. Reject `$` and backtick (and newline/CR/NUL) entirely at the boundary.
+// `remotePath`/`identityFile` are shell-escaped, and a remote launch reaches `bash -c`
+// single-quoted (`bashCArg()` in tmux-manager). They are also pasted into strings the
+// far end's shells parse, and hosts stored before a launch-quoting change are read with
+// no schema, so `$` and backtick (and newline/CR/NUL) stay rejected at the boundary as
+// defense in depth, whatever the current quoting does with them.
 const NO_SHELL_META = /^[^\n\r\0`$]*$/;
 
 export const RemoteHostSchema = z.object({
@@ -982,10 +982,10 @@ export const RemoteCaseLinkSchema = z.object({
 //
 // Docker mode is a location overlay on cases (see docs/docker-cases-plan.md),
 // the analog of the remote-SSH schemas above. `image`, `hostWorkspacePath`,
-// `containerWorkdir`, and `container` all reach the outer `bash -c "..."` launch
-// layer, so they carry NO_SHELL_META (rejects `$`/backtick that survive the
-// double-quote layer) exactly like remotePath/identityFile. `--privileged` and
-// any docker-socket mount are structurally unrepresentable (never accepted).
+// `containerWorkdir`, and `container` all reach the `bash -c` launch layer, so they
+// carry NO_SHELL_META (rejects `$`/backtick) exactly like remotePath/identityFile.
+// `--privileged` and any docker-socket mount are structurally unrepresentable
+// (never accepted).
 
 const DockerResourceLimitsSchema = z
   .object({