Migrate GraphExecutor onto the OpenRegister flow engine

[rubenvdlinde]

hermiq shipped its own graph engine (lib/Service/Graph/GraphExecutor.php, #30). It is the sixth system in this fleet called "flow", and exactly what ADR-022 exists to prevent — the OpenRegister flow-engine proposal names five others and we added one more.

It should become a consumer.

What changes

• GraphExecutor is replaced by OCA\OpenRegister\Service\Flow\FlowEngine.
• hermiq contributes a FlowStepDispatcher handling the step types it owns:
  • agent-step — run an agent turn (the thing only hermiq can do)
  • Its condition / router / object-write steps are dropped in favour of the engine's own If/Switch and object steps (openregister#2067).
• The canvas (GraphBuilder.vue / GraphSidebar.vue) moves to the shared flow builder, keeping CnGraphCanvas underneath.
• Saved agentflow objects migrate to the flow document shape. The engine already accepts the {source, target} dialect CnGraphCanvas emits, so the edge format needs no translation.

What hermiq keeps

The agent step, and only the agent step. That is the genuinely hermiq-specific capability; graph walking, branching, item handling and run tooling are not.

Watch for

• The item-list contract (openregister#2064): an agent step becomes items-in/items-out, so an agent step naturally runs once per item. GraphExecutor's single flat state has no equivalent and its {{key}} placeholders become JSONLogic expressions (openregister#2069).
• agentId vs agent — both are honoured in the current executor; the migration is the moment to settle on one.
• The trace shape shipped in feat: Vue 3 migration + visual flow builder for agent graphs #30 (produced / passed per step) is close to what the engine's run log needs, and should inform openregister#2070 rather than being re-invented.

Depends on openregister#2064.