#4708 Docs: reaching swamp start and swamp dashboard from another machine (--host)

swamp-club#4707 adds an opt-in --host flag to swamp start and swamp dashboard (default 127.0.0.1), and --port and --trusted-hosts to swamp start.

Pages to update in content/manual:

• how-to/start-a-task-with-swamp-start.md: the SSH paragraph says to pass --no-browser and open the printed URL, which cannot work because the page listens on 127.0.0.1 only. Replace with: run swamp start --no-browser --host 0.0.0.0 and open one of the printed From another machine URLs; the page is then reachable by anyone on the network who has the link, over plain HTTP; a name that is not the machine's own (FQDN, Tailscale) needs --trusted-hosts; a host firewall (e.g. the macOS application firewall) may need to allow swamp; launches show a command to copy instead of opening a terminal window.
• reference/swamp-serve/dashboard.md: add --host next to --port and --trusted-hosts.
• reference/workspace-commands.md (if it lists swamp start flags): add --host, --port and --trusted-hosts.