HAF 1.28.7

Emergency point release for the 2026-07-09/10 incidents:

- fix hive.remove_obsolete_reversible_data destroying shared-fork blocks
  before they were copied to the irreversible tables (#333) -- the cause
  of the fk_1_hive_irreversible_data crashes and WAL crash-loops that
  downed at least eight mainnet HAF nodes
- hive submodule updated to the tagged 1.28.7 release (p2p fork-tolerance
  fixes, hive!2064/!2065)
- pin pg_cron to v1.6.7 (upstream master broke glibc builds)

No schema changes; in-place extension update; no replay required when
upgrading from 1.28.6-era builds.  Operators of nodes that crashed or
'recovered by restart' should see issue #333 for the recovery runbook and
the silent-hole audit probe.