Persist facts (provided artefacts, condition values) in the store so set can record them #35

The domain's Facts port answers which input artefacts are provided (artefactKey) and the values decision conditions read, but nothing persists those answers. The store contract keeps a model and its overlay only, so the CLI's set (which the plan wrote as set <artefact> <value>) can set an element's run state but cannot record that an artefact was provided or that a condition's fact holds. Today CliPorts.facts defaults to a port that knows nothing, so a consumer of an input artefact stays blocked and every conditional branch stays unknown unless a host injects its own facts.

What is needed: facts stored per model beside the overlay (a facts.set procedure, facts returned by models.load, a migration in graph-store-sqlite, the fake and the conformance kit), then set in graph-cli writing artefact provision and fact values, and the CLI building its Facts port from the stored facts.

Deferred from the graph-cli PR (#34) because it changes the store contract, its SQLite adapter and their conformance kit, which is a store-layer change of its own.

Revisit trigger: the first model synced or authored with an input artefact or a decision condition, or the graph-cli PR merging, whichever comes first.