Add a troubleshooting entry for Hosts that lag behind on blocks.

[johnnymatthews]

One user in Discord had just stood up a Host, and the sync question came with it. The team's guidance: you don't need to do anything manually, the Host catches up with the blocks it receives from the Generator on its own, and the Generator itself may lag behind the chain, which is already being worked on.

None of that is written down anywhere. The troubleshooting page has "My Host client starts but connects to no peers" and the dashboard offline entries, but nothing about a connected Host that's behind on blocks. An operator watching lag can't tell "this catches up by itself" from "something's broken" without asking in Discord.

• Add a Host entry covering expected catch-up behavior after startup, and lag that traces back to the source Generator.
• Keep the Generator-lags-too part time-neutral, or link to wherever release notes live, so the entry doesn't go stale when the lag fix ships.
• Check whether this belongs in Add Operator Lifecycle Content #316 (operator lifecycle content) instead of the troubleshooting page.