feat(serve): node name, LAN IP hints, and token URL auto-login

[RealZST]

Summary

Improves the hk serve web-mode experience when working with remote or multiple nodes.

• Node name — hk serve --name <label> (defaults to the machine hostname), exposed via a new GET /api/server_info and shown in the sidebar and the browser tab title. When several browser tabs each point at a different machine, you can tell them apart at a glance.
• LAN access — when bound to 0.0.0.0, print the machine's actual LAN IP(s) instead of the unreachable 0.0.0.0 address.
• Token auto-login — embed the access token in the printed URL (?token=…); the frontend reads it on load, stores it, then strips it from the address bar via replaceState (the same pattern Jupyter uses). Previously a non-localhost bind required a token but the web UI had no way to supply one.

Relates to #39

#39 raises the cross-device case: managing agents on several machines means juggling browser tabs and wanting an "所属主机" (host) label to know which machine is which. This adds that per-node label (sidebar + tab title) so multiple tabs are easy to distinguish. The broader aggregation dashboard and cross-host deploy from #39 are out of scope here.

Testing

• Rust — server_info endpoint test; full hk-web suite green.
• Frontend — vitest for consumeUrlToken (store + strip + preserve other params); tsc and biome clean.
• Manual (macOS) — --host 0.0.0.0 prints real LAN IPs + a ?token= URL; opening it auto-logs-in and the token disappears from the address bar; sidebar and tab title show the node name; clearing the token yields 401s.

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