Server-side auto-mode dangerous-tool-use classifier

Auto mode's server-side dangerous-tool-use classifier is expanded: API requests now carry a safeguards: [{ type: "dangerous_tool_use", context }] field, riding on a new anthropic-beta header entry, and the response's streaming deltas are parsed for matching safeguard_results against a schema of per-tool-call outcomes (flagged, not_flagged, skipped, unavailable). When flagged, the action is blocked with reason 'The server-side auto mode classifier judged this action dangerous'; if the server call is unavailable or times out, it blocks for safety with 'Classifier unavailable - blocking for safety'. The auto-mode fast-path check can now await a server classifier result and fall back to asking the user if the classification changed while queued (mode_changed_while_queued), recording telemetry fields classifierSource: server and serverClassifierNoVerdict, and a tengu_auto_mode_fallback_to_ask event.