[Feature]: Emit Normal events on phase transitions across all six reconcilers

Follow-up to #150. Failure-path Warning events now exist at every tier: a331c85 wired the Job and Workflow reconcilers, and #250 wired Certification, GoodputMeasurement, BandwidthMeasurement, and WorkloadRun. What remains from #150 is the other half: events on key state transitions (InProgress, Succeeded, Failed) so kubectl describe tells the lifecycle story without controller log access.

This needs real design, which is why it was split out:

• Transition events must fire once per actual transition, not once per 15s requeue. Every reconciler funnels condition changes through setExclusiveCondition (pkg/controller/status.go), which already knows whether the condition actually changed, so that is the natural hook for dedup.
• The integration harness (cmd/integration/integration_test.go) currently wires a recorder only for the Workflow reconciler; asserting on emitted events would need harness support and golden coverage.
• Decide which transitions matter per tier. A Normal event per phase at six tiers is roughly 18 sites; some (measurement Complete, Job iteration restarts) may not be worth the etcd traffic.

Events RBAC is already in place, and every reconciler now has a nil-safe event helper, so this is purely about placement and dedup.

Also worth picking up here: the two Certification build/validation failure paths before Workflow creation (around certification_controller.go lines 188 and 252) still emit no Warning event. Both go terminal via setCertificationFailed, so a one-shot event there is safe and could reuse ReasonWorkflowValidationFailed.