KAI OS v0.1.77

Agent Gate product hardening release.\n\n- Added evidence.diff.changes so machine-readable evidence includes sampled stable runtime differences.\n- Agent Gate Step Summary now includes a What Changed table when --baseline ... --check detects behavior changes.\n- Evidence text output now prints sampled changes alongside the difference count.\n\nVerification: ./gradlew test installDist distZip distTar --no-daemon; scripts/quickstart-smoke.sh; YAML parse; manual baseline-diff gate --summary-out smoke.