[KeyffMS]

R2i

Small move-only continuation of #83 R2.

Scope:

• move only ApplicationState construction/accessor implementation (Default, with_registry, with_registry_and_suggestions, registry, session) from application.rs into the existing application/state.rs;
• keep the single public ApplicationState definition and top-level ApplicationState::reduce in application.rs;
• preserve the existing public API and behavior.

Safety/architecture:

• write/restore exact operator-confirmation paths remain unchanged in application.rs and remain directly covered by the existing architecture gate;
• no reducer authority, session/write authority, scheduler/budget/fairness/QueueFull, filesystem boundary, or conformance semantics changed;
• no gate/test weakening.

Refs #83