[Meta] Extend work across hosts and devices #58

Work across hosts and devices, beyond the dogfooding backlog in #5. Items are ordered by importance.

• Let agents discover and message channels on peer hosts #57: agents discover and message channels on other hosts, both local and hosted (Let hosted agents discover and message team channels #180 folded in).
• Reach teammates' terminals through the gateway #11: terminals from the owner's other machines, from teammates, and in cloud containers.
• Move a channel to another host so work can continue on that machine #49: move a whole channel (state and files) to another Mac. After Universe.
• Verify real-phone use and address mobile gaps #18: verify real-phone use.

Hosted channels (the #13 meta is closed; these are standalone issues):

• Create hosted channels from the new-channel picker #177: create hosted channels from the new-channel picker.
• Manage hosted channels while their workspace is offline #179: manage hosted channels while their workspace is offline.
• Recover channel moves from interruption and retries #429: recover channel moves from interruption and retries.
• Reach hosted channels from a browser without a host gateway #182: browser access without a host gateway (later).

Cloud compute (the #216 pilot is done):

• Keep a cloud channel's listing in step with its compute service #430: show the stopped state after the service's idle stop.
• Preserve and recover cloud workspace files beyond the pilot checkpoint limit #413: keep workspace files beyond the checkpoint limit and across the idle stop.
• Let channel agents inspect compute usage and request bounded resizing #414: let agents see compute usage and request a bounded resize.