revert(bash): drop the executor dialect guard

The ShellDialect marker on BashExecutor and the load-time rejection in
tool-bash/tool-pwsh force every test and example fake executor to declare
a dialect for a guard with no in-repo or plausible deployment to catch
(shipped compositions always pair the tool with its matching executor),
and they break the example composition suites that stub ctx.bash without
a dialect (agent-spine-demo/cli-demo/acp-demo lost the bash tool).

Keep the non-dialect doc fixes that landed with the attempt: the tool-bash
README bashEnv contract trim with the stale example import removed, the
acp-snapshot suite.ts 'usable pwsh' JSDoc, and the pwsh.cordis.yml comment
indent. The parity note records the attempt and revert under Alternatives.

packages/bash/tool-bash/src/index.ts

@@ -188,11 +188,6 @@ const BACKGROUND_OUTPUT_PROPERTIES = {
 } as const
 
 export function apply(ctx: Context, config: Config = {}): void {
-  // Model commands are written in bash; a mismatched executor would hand
-  // them to another shell's parser and surface as ordinary nonzero exits.
-  if (ctx.bash.dialect !== 'bash') {
-    throw new Error(`tool-bash: the mounted executor speaks '${ctx.bash.dialect}', not bash — mount a bash executor (e.g. dsh-bash-local) or the matching shell tool`)
-  }
   const backgroundEnabled = config.enableRunInBackground ?? true
   const defaultMode = ctx.bash.sandboxMode
   const escalationModes: readonly SandboxMode[] = defaultMode === undefined ? [] : ESCALATION_TARGETS