- Extend cmdStatePrune to prune Performance Metrics table rows older than cutoff
- Add workflow.auto_prune_state config key (default: false)
- Call cmdStatePrune automatically in cmdPhaseComplete when enabled
- Document workflow.auto_prune_state in planning-config.md reference
- Add silent option to cmdStatePrune for programmatic use without stdout
Closes#2087
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>