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/bash-local/src/index.ts

@@ -80,8 +80,6 @@ function assertPositiveFinite(name: string, value: number): void {
 export class LocalBashExecutor extends BashExecutor {
   static inject = ['subprocess']
 
-  readonly dialect = 'bash' as const
-
   static Config: z<Config> = z.object({
     cwd: z.string(),
     timeoutMs: z.number().default(120_000),