Workflow 2.4.3

Dashboard trends now aggregate completed and failed counts in the database,
and median duration selects the middle value without loading every duration.

Adds an opt-in boundedDashboardSummary() observer method that defers complete
history audits. Unevaluated audit counts are null with
history_audit_evaluation: not_requested. Existing dashboard and metrics APIs
retain their full audits.

Qualified on SQLite, MySQL, PostgreSQL and MariaDB, with supported Laravel
upgrade checks and the complete unit and coverage gates passing.
Source checks.

Waterline adoption is in Waterline #142,
with the standalone Server endpoint in Server #305.
Workflow execution and portable worker protocols are unchanged.