application: channels bounded context

CQRS use cases (create/update/delete/get/list/list_by_owner),
ownership checks, auto-snapshot on config change.
Channel setters added to domain model.

crates/application/src/channels/queries.rs

@@ -0,0 +1,14 @@
+use uuid::Uuid;
+
+/// Fetch a single channel by ID.
+pub struct GetChannelQuery {
+    pub channel_id: Uuid,
+}
+
+/// List all channels.
+pub struct ListChannelsQuery;
+
+/// List channels belonging to a specific owner.
+pub struct ListByOwnerQuery {
+    pub owner_id: Uuid,
+}