Start Cloud chats in per-chat folders
TE
4d ago+318+318+012345678901234567890123456789-78-78-01234567890123456789
A Cloud chat started without a selected folder now starts immediately in a fresh private ~/chats/<chat-id> folder on its Cloud machine. Swift forwards an omitted cwd for this case; Rust owns folder selection, creation, and trust. The peer path uses the same durable Cloud folder while non-Cloud starts retain their required-folder and /tmp scratch behavior.
This implements Leo's request: “i want us to be able to do this too” for a Cloud chat with no project, where the agent starts right away on an empty machine.
Validation: targeted Rust tests and Swift compile checks are being run through the fleet after opening this PR.
Agent session: agent session