enh(tools): adversarial policy gate not shown in /status output

[bug-ops]

Observation

When [tools.adversarial_policy] enabled = true is configured, the /status slash command does not mention the gate. All other security layers (tool filter, trust gate, policy enforcer) are visible in /status; the adversarial gate is silent.

Expected

/status should include a line like:

Adversarial gate: enabled (provider=openai-stt, policies=2, fail_open=false)

Current

No mention of adversarial policy in /status output.

Steps to reproduce

1. Add [tools.adversarial_policy] enabled = true to config
2. Run /status
3. Observe: no adversarial gate line

Fix sketch

Add adversarial policy status to format_status_message() in zeph-core/src/agent/slash_commands.rs. The gate config is accessible via AgentConfig::tools.adversarial_policy.