Closes #2150

What

Adds an opt-in background prewarm for recallMode=tools that fetches a small user snapshot (representation + peer card) from Honcho on /new or session reset, and injects it into the first real turn's user message.

How

• HonchoClientConfig: new tools_startup_context: bool = False field (JSON key: toolsStartupContext)
• HonchoSessionManager.fetch_startup_snapshot(peer_id): fetches user representation + peer card without requiring an active session in local cache
• run_agent.py: _schedule_honcho_startup_prewarm() fires a daemon thread on session init; _pop_startup_snapshot() consumes it once on first turn
• cli.py: prewarm triggered in new_session()
• gateway/run.py: prewarm triggered after reset, _honcho_startup_cache keyed by peer_name

Design decisions

• Injected via _honcho_turn_context (user message append), not _honcho_context (system prompt) — prompt cache prefix stays stable
• pop() semantics — consumed exactly once, subsequent turns unaffected
• not conversation_history guard — first turn only
• Keyed by peer_name (stable Honcho identity), not ephemeral session ID
• V1 scope: representation + peer card only. No dialectic, no AI peer context, no continuity recall

Not included (by design)

Continuity-style recall is intentionally excluded per issue spec — /new semantically means a fresh session.