#29109 Cloud start: no Cloud default in a fresh SSH or peer tab; translate the Start New Chats In: Cloud choice

Follow-up to #29669, which carried this PR's feature (Settings > General > Agent Chat > Start New Chats In: This Mac / Cloud) onto feat-cmux-next. After merging base, this PR keeps base for everything #29669 landed and adds only two things on top:

1. No Cloud default in a tab on another machine, even before its summary arrives (#29144). With Start New Chats In set to Cloud, a fresh SSH or peer tab could pick the Cloud run default before its summary said it was remote, so its first send would go to cloud.startChat, which the host refuses there. webviews/src/agent-session/acpmux/App.tsx now also reads the snapshot's origin (remote or peer), which a fresh connection has before any summary.
2. The Cloud choice translated. settings.choice.newChatsInCloud was "Cloud" in every locale; it now has a translation in each (still needs_review). de, fr and it keep "Cloud", with the reason recorded in scripts/localization-allowed-omissions.json.

agentPane.newChatsIn stays refused to agents, the way base has it (.privacy in the agent policy, agent_settable: false in schemas/settings/settings-schema.json). The branch's earlier commit that let agents set it is gone in the merge: an agent could have sent future chats to Cloud, which goes against the setting's privacy policy (review BLOCK at 64edec6c). The merge also keeps #29582 (cloud.startChat's pick moved into cmux-tui; this branch's now-unused chats-machine name helpers are dropped), #29785, #29789, #29771 and #29529's eased-follow test tolerance.

Leo, 2026-10-31: "whenever i start a chat it should be able to send me to cloud autommatically keep launching/downloading new dev builds and such".

Risk: small. One web conditional and localization data. No Swift source changes compared with base.

Agent session: agent session
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