Add State v2 guard and DI integration demos to State sample

[Skymly]

Summary

• Extends DesignPatterns.Samples.State to demonstrate State v2 features:
  • Guard delegates: [Transition] Guard property with CanCancelDraft / CanCancelSubmitted static guard methods on the holder class
  • DI integration: generated RegisterDi method + AddTransitionTable extension, resolving ITransitionTable<OrderStatus, OrderTrigger> from ServiceProvider
  • GetAllowedTriggers: shows allowed triggers per state and terminal state (Paid has none)
• Adds Cancelled state and Cancel trigger for richer edge coverage
• Changes DesignPatternsSampleKind from Core to DependencyInjection to pull in DI extension and enable DesignPatterns_EnableDiIntegration

Sample output

=== Manual TransitionTableBuilder (with guard) ===
  Draft + Submit -> Submitted
  Submitted + Pay -> Paid
  Draft + Cancel -> Cancelled
  Paid + Pay is invalid (expected).

=== Generated [StateMachine] table (with guard) ===
Initial state: Draft
  Draft + Submit -> Submitted
  Submitted + Pay -> Paid
  Draft + Cancel -> Cancelled
  Submitted + Cancel -> Cancelled
  Paid + Pay is invalid (expected).

=== DI integration (RegisterDi + AddTransitionTable) ===
Resolved from DI: OrderStatusTransitionTable
DI table initial state: Draft
  Draft + Submit -> Submitted
  Submitted + Pay -> Paid
  Cancelled + Submit is invalid (expected).

=== GetAllowedTriggers ===
Allowed triggers from Draft: Submit, Cancel
Allowed triggers from Submitted: Pay, Cancel
Allowed triggers from Paid (terminal): (none — terminal state)

Test plan

• dotnet build DesignPatterns.Samples.State -c Release — 0 warnings, 0 errors
• dotnet run --project DesignPatterns.Samples.State -c Release — output matches expected