Add soak test suite: diagnostics + compressed workload + CI jobs

CBM_DIAGNOSTICS=1 writes /tmp/cbm-diagnostics-<pid>.json every 5s.
scripts/soak-test.sh: compressed workload + crash recovery + analysis.
CI: soak_level input (full/quick/none) on dry-run + release.
MCP query timing via cbm_diag_record_query().