Introduce Poly.DomainModeling.V2 immutable domain core with mutation sessions and MCP-oriented authoring tools

[Copilot]

This PR adds a new Poly.DomainModeling.V2 foundation for UI/API/MCP consumers with an immutable domain model, unified mutation shape, and session-based mutation workflow. It establishes a clean v2 surface for future domain modeling evolution while keeping analysis, rendering, and validation first-class.

• Immutable V2 domain primitives

  • Added immutable records for Domain, DomainType/Entity, Property, Stage, Action, Relationship.
  • Added IEffect hierarchy with concrete effects: SetProperty, TransitionStage, CreateEntity, InvokeAction.
  • Added relationship kind modeling via RelationshipKind.

• Builder + DSL authoring surface (internals-backed)

  • Implemented internal fluent builders (DomainBuilder, EntityBuilder, ActionBuilder) with nested lambda composition.
  • Added public DSL entrypoint via DomainFactory.Create(...) and DSL wrappers (DomainDsl, EntityDsl, ActionDsl).

• Unified mutation contract

  • Added DomainMutation + DomainMutationKind as a single mutation payload model for API/MCP workflows.
  • Implemented mutation application in DomainMutationEngine with immutable updates and validation enforcement.

• Session lifecycle and traceability

  • Added DomainSessionManager with CreateSession, Mutate, and GetTrace.
  • Added revisioned session state (DomainSession) and mutation history (DomainTraceEntry).

• MCP-style high-level operations

  • Added DomainMcpTools.CreateEntityWithPattern(...) for opinionated entity bootstrapping.
  • Added DomainMcpTools.AddCRUD(...) for standard action/effect scaffolding.

• Analysis / rendering / validation support

  • Added DomainValidator, DomainAnalyzer, and DomainRenderer to keep quality and inspectability strong in the v2 surface.

• E-commerce demo + focused tests

  • Added DomainModelingV2ECommerceDemo showing both DSL-first and session/mutation-driven composition.
  • Added v2-focused tests covering immutable DSL construction, session mutation trace flow, MCP helpers, and analysis/render/validation behavior.

using Poly.DomainModeling.V2;

var domain = DomainFactory.Create("ECommerce", d => d
    .Entity("Order", e => e
        .Property("Id", "Uuid", isRequired: true)
        .Stage("Draft", isInitial: true)
        .Action("Ship", a => a.Effect(new TransitionStage("Shipped"))))
    .Relationship("CustomerOrders", "Customer", "Order", RelationshipKind.OneToMany));

var sessions = new DomainSessionManager();
var session = sessions.CreateSession("ECommerce");
session = sessions.Mutate(session.SessionId, DomainMutation.AddEntity("Customer"));
var trace = sessions.GetTrace(session.SessionId);

Original prompt

Create a new simplified domain modeling system from scratch in Poly.DomainModeling.V2 (or similar) following this exact vision for UI/API/MCP consumers only: Immutable core records for Domain, DomainType/Entity, Property, Stage, Action, Relationship, IEffect hierarchy (SetProperty, TransitionStage, CreateEntity, InvokeAction, etc.). Internal DomainBuilder with fluent nested lambdas. Unified DomainMutation record for API/MCP. Session management with CreateSession, Mutate, GetTrace. High-level MCP tools (CreateEntityWithPattern, AddCRUD, etc.). Keep analysis, rendering, validation strong. Base it on the rewrite/domainmodeling-from-scratch branch. Include e-commerce demo. Make it the foundation for future great domain modeling.