New resume telemetry for first-turn announcements

Telemetry is usage data Claude Code reports back. Two new events were added around resuming, which means reopening an earlier conversation:

• tengu_resume_first_turn_announcement_census is sent every time a session is loaded for resume.
• tengu_chain_first_turn_announcements_off_chain is sent once per session file while the conversation's message chain is rebuilt.

Both measure context entries, such as instructions, the date and session context, that end up outside the message chain around the first turn.