fix(zarvis): time out idle provider turns

[edwin-zvs]

Summary

• add a zarvis provider idle watchdog around model turns
• route both interactive and headless provider calls through the watchdog
• add regression tests for hung provider completion and disabled timeout

Behavior

If a provider turn produces no visible text/reasoning and never completes, zarvis now emits a provider error instead of staying permanently Running. The default idle timeout is 600s (10 minutes) and can be disabled with AGENTD_ZARVIS_PROVIDER_IDLE_TIMEOUT_SECS=0.

Tests

• cargo test -p agentd-adapter-zarvis provider_watchdog -- --nocapture
• cargo check -p agentd-adapter-zarvis
• cargo test -p agentd-adapter-zarvis
• cargo build