place dsl

[matt-beanland]

Add places DSL.

This means:

• adding a Place extension, with instances, places and parties
• extending Instance extension with places
• extending Party extension with places

Also consider related Instance Party and Place behaviours

[matt-beanland]

Closes with more scope than originally planned — in a good way.

The card started as "add a Place DSL" but the right first move was a pure refactor: extract BasePlace as a Spark.Dsl.Fragment following the BaseParty pattern, simplify Diffo.Provider.Place to use it, and verify zero regressions before touching the DSL. That discipline paid off — every subsequent step landed cleanly.

What shipped:

BasePlace fragment with label :Place (critical for Neo4j relationship wiring — would have been a runtime mystery without tests catching it)
Place.Extension with instances do, parties do, places do sections; persisters baking instances/0, parties/0, places/0 onto resources; VerifyRoles verifier across all three sections
places do added to Instance.Extension structure do and Party.Extension, with matching persisters and place/1 generated on instance resources
Four test fixtures demonstrating the simple and complex patterns for both Party and Place: Organization, Carrier (:abn, :trading_name), GeographicSite, ExchangeBuilding (:nli, :access_type)
Moduledocs updated across BaseInstance, BaseParty, BasePlace — including an explicit "Domain-specific attributes" contract section explaining why domain attributes need a custom action
Livebook rewritten with a full Place Extension section, DataCentre domain resource, and cluster creation simplified to use the domain API directly
583 tests, 0 failures (up from 521 at the start of the branch)