v2.5.0-beta.202606221048

Add INFO-level progress logging to the cross-major migration engine

A 14->18 migration on a large data tank can run for over an hour, but the
engine only logged at TRACE (off by default) and WARN, so an operator saw
almost nothing between `service start` and the final status file. Add INFO
lines at each engine milestone (start, dump, restore-complete-at-tier,
validate, commit) and at each restore tier (reserved-word route, tier 1
parallel, tier 2 serial escalation, tier 3 per-table COPY, tier 4
per-partition COPY), with per-table progress in the COPY tiers and a periodic
per-partition counter for tables of 500+ partitions. Logging only; no
behaviour change.