[iamnbutler]

Adds a second hosting option for the team's services, alongside Cloudflare. On Fly.io, each service runs as a single celld node with its own Tigris bucket, deployed with `services/fly.toml`. Both services share that one file. Each Fly app sets `CELLD_BUCKET` as a secret, and the bucket keys from `fly storage create` are saved on the app automatically. The code deploys from a checkout with `services/celld.ts` (from #537). `docs/setup.md` has the steps.

Config choices:

• The node never auto-stops, because alarms and sleeping sockets need it running.
• `CELLD_DURABILITY=bucket`: with no peer node, the bucket is the only copy of each write.
• `kill_timeout` is set above celld's 40 s shutdown bound, so a stop can save and hand off its cells.
• The health check uses `/.well-known/celld/health`.
• The image is pinned to the githubnext/celld fork, which carries the fix for Fix async operations resumed from continuations of retired events denoland/celld#277.

Tested with the apps `ace-fly-directory` and `ace-fly-channel` in iad:

• A separate Ace host joined the directory and saw the Fly channel service offered as `hosted`.
• It created a hosted channel that read the README and ran `git log` in the workspace.
• After a machine restart, the channel still answered from its earlier conversation.
• After a redeploy, it ran `ls`.
• No errors in the Fly logs.

Built in Ace

No. This was built with Claude Code in a terminal, continuing the celld session from #537. `flyctl` and the Fly dashboard were used for the account, apps and buckets, because Ace doesn't provision hosting. Tracked under #5.