JasperFx 2.54.0

Two additive features for the Spec Driven Development track (master: JasperFx/stoat#9). Minor rather than patch because both add public surface; nothing existing is removed, renamed or obsoleted, and every existing constructor and JSON payload round-trips unchanged.

Event Modeling semantic model v2, overlay API and discovery bridge (#687, #689 — PR #691)

JasperFx.Events.EventModeling is now the one slice vocabulary every source writes into and every viewer reads from:

• EventModelSliceDescriptor keeps its positional shape and gains Pattern (SlicePattern: Command / View / Automation / Translation), TriggerKind (Http / Grpc / MessageHandler / JobScheduler / Human / External), TriggerOrigin, AggregateTypes (a list — one handler may load several projected models), PublishedMessages, ExternalSystems, Hotspots, Specifications (typed: {Feature}/{Scenario} identity + resolved types, stamped by sources), Domain, plus the computed rendering contract Elements (stable id, kind → canonical colour, lane) and Edges (directed, by id), and Merge(other).
• EventModelDescriptor gains Aggregates and a static Merge(name, descriptors).
• HandlerRelationshipDescriptor.ToSliceDescriptor() folds the older handler-relationship vocabulary into a slice.
• The fluent API is an overlay: EventModelDefinition / EventModelBuilder / EventModelSliceBuilder name, group (InDomain), annotate (TriggeredBy(label)) and link (LinksToSpecification) — roles are derived by the sources that can see them. The role-declaring methods live behind one documented escape hatch, ForFlowNotOwnedHere(...).
• The discovery bridge: EventModelDefinitionSource, services.AddEventModel<T>() / AddEventModel(type | instance | name, lambda) / AddEventModelsFromAssembly / AddEventModelSource, and EventModelDiscovery.DiscoverAsync / AssembleAsync. IEventModelDefinitionSource finally has implementations.
• #689: HotspotDescriptor.PendingSpecification(specIdentity) — a pending specification renders as a hotspot on the slice it binds to.

ProjectionScenario exposes its plan and observes each step (#688 — PR #692)

ProjectionScenario<TOperations, TQuerySession> gains PlannedSteps (number, kind, description — readable before ExecuteAsync) and an Observer (IProjectionScenarioObserver: StepStarted / StepSucceeded / StepFailed / StepSkipped), numbered as the exception report numbers them. Marten, Polecat and Fisher subclasses need no change.