[KeyffMS]

R2l

Small move-only continuation of #83 R2.

Scope:

• move only ApplicationState::csv_stop_effect and ApplicationState::translate_session_effects from crates/lantern-app/src/application.rs into new private crates/lantern-app/src/application/session.rs;
• keep exactly one public ApplicationState definition and the top-level ApplicationState::reduce in application.rs;
• relocate only the imports used by those helpers.

Safety/architecture:

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

Acceptance:

• keep draft until full immutable CI is green on the exact PR head;
• after merge, require green post-merge CI on the exact merge SHA before marking R2l DONE.

Refs #83