Update flow fields

Field-level update. Every field is optional; only what you send changes.

internal_version is required alongside config: it is checked against the stored value so a graph edit is refused rather than silently overwriting someone else's concurrent edit. Read it from GET /flows/{flow_id}.

FlowOut plus the pieces an editing client needs.

Without config and internal_version a caller cannot do a read-modify-write at all, which is why the API could only run flows.