Auto mode billing notice: shown in SDK hosts, and moving on no longer counts as consent

What

When auto mode cannot use server-side review, it can fall back to making its own classifier requests, which are billed. A notice warns about this first. Several changes affect that notice:

• It can now be shown when Claude Code runs inside an SDK host (another program that embeds Claude Code), provided the host says it supports the auto_mode_server_fallback dialog and the tengu_expressive_galaxy flag is on. That flag's built-in default is on. Before, the notice was always skipped in SDK hosts.
• The dialog gains a description entry asking you to acknowledge the classifier billing notice, with Enter continuing in auto mode. Its data must now include title, paragraphs and helpUrl alongside gatewayHost, so remote and headless hosts show the same text as the terminal.
• When there is nowhere to show the dialog, Claude Code continues silently and logs a debug line.
• If you move on without answering, the notice now returns continue_unacknowledged: work carries on, the remembered fallback choice is cleared so the notice can come back, and no billing acknowledgement is recorded. Only an explicit continue records one.
• If the turn is stopped while the notice is showing, it returns "interrupt".
• The notice's record now notes whether it ran in an SDK host.

Why

People using Claude Code through SDK hosts or desktop apps can now be warned before classifier requests start being billed, and ignoring the notice is no longer treated as agreeing to the charge. Nothing has been read about tengu_expressive_galaxy, so whether the SDK-host notice is active is unknown.