docs: attribute the hasPwsh probe to the caller and name the bash dialect

Round-four nits: the acp-snapshot README said 'the suite's hasPwsh probe
follows the executor's own resolution' — hasPwsh is caller-supplied, and the
resolvePwshPath-following behavior belongs to the shipped acp-agent caller;
reword to 'the caller-supplied hasPwsh probe (the shipped acp-agent suite
follows the executor's own resolution...)' on both language sides. And the
tool-bash README loses its only explicit pairing sentence with the dialect
guard reverted, so state the contract plainly: 'The tool contract is
bash-dialect — mount a bash-parsing executor' (both languages, pairing
re-recorded).

packages/bash/tool-bash/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/bash/tool-bash/README.md
-README.md: f21b6b4344fcfb94d88f1f7e1c4444ee89e0ead8
-README.zh.md: c9dd3f2250631f3300edaf2c246e6925f3e12005
+README.md: 35a5647365dab6daa903c14cba8b83702b50305d
+README.zh.md: eb7901f3445117988d77e6d39b73681480b7a754