v1.2.7

• breaking: qexp now defaults to the v2 shared-root engine; the v1 single-machine engine is still available via --v1 flag or QEXP_VERSION=1 environment variable
• feat: qexp v2 — shared-root multi-machine experiment queue with explicit machine identity, CAS-based concurrency, batch support, retry lineage, on-demand agent, and scheduling events
• feat: qexp v2 subcommands: init, submit, cancel, retry, batch-submit, batch-retry-failed, batch-retry-cancelled, list, inspect, top, batches, batch, machines, logs, clean, agent start/stop/status, doctor verify/rebuild-index/repair-orphans/cleanup-locks
• deprecation: qexp v1 engine is deprecated and will be removed in v1.3.0
• docs: add qexp user manual and release workflow checks that publish changelog-backed release notes