v0.7.0 — definitions render themselves

Additive release, no breaking changes.

WorkflowDefinition::toGraph() — every definition can now serialize itself into a renderable graph: rows of typed nodes plus labelled edges (yes/no on condition branches, fan-out on parallel branches), with node details for display (agent targets, prompt previews, await reasons and schemas, evaluator budgets). The payload includes the definition hash, so consumers can detect drift against a run's pinned version.

First consumer: the new timmcleod/agent-workflows-ui dashboard package, which renders runs as live flowcharts over this graph.

Also: created_at/updated_at are now declared on the WorkflowRun and WorkflowInterrupt docblocks, so static analysis in consuming apps no longer flags reads of them.