feat(session-limits): LS3 — port Scheduler + adapter TokioScheduler

Introduit l'abstraction de planification pour la reprise différée à la
levée d'une limite de session :
- domaine : trait Scheduler + enum ScheduledTask (ports.rs), ScheduleId
  via typed_id! (ids.rs), re-exports (lib.rs).
- infra : TokioScheduler (scheduler/mod.rs, nouveau) + pub mod scheduler
  et re-export (lib.rs).

Tests QA inline (#[cfg(test)]) : 7 tests scheduler (3× sans flaky).
`cargo test -p infrastructure` = 195 passed / 0 failed ; domaine + infra
builds 0 warning ; LS1/LS2 toujours verts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/domain/src/ids.rs

@@ -92,3 +92,10 @@ typed_id!(
     /// Identifies a node in a [`crate::layout::LayoutTree`].
     NodeId
 );
+typed_id!(
+    /// Identifies one armed one-shot wake-up of a [`crate::ports::Scheduler`]
+    /// (ARCHITECTURE §21.4). Opaque, cancellable handle returned by
+    /// [`crate::ports::Scheduler::arm`] and consumed by
+    /// [`crate::ports::Scheduler::cancel`].
+    ScheduleId
+);