Move events back into interface-class source files (restore #3975 placement)

Reverses the earlier dedup-by-re-export: event TYPE definitions now live in the
interface classes, and the emptied decomposed event files are removed.

- MessageSeenEvent            -> logos_delivery/api/kernel_api.nim
- Message{Sent,Error,Propagated,Received}Event -> api/messaging_client_api.nim
- ChannelMessage{Received,Sent,Error}Event     -> api/reliable_channel_manager_api.nim
- EventConnectionStatusChange -> api/logos_delivery_api.nim

Deleted (became empty after the move):
- logos_delivery/waku/api/events/message_events.nim
- logos_delivery/messaging/api/events.nim
- logos_delivery/channels/api/events.nim
health_events.nim keeps its two remaining events (content/shard topic health).

Rewiring: each layer re-exports its interface module (waku->kernel_api,
messaging_client->messaging_client_api, reliable_channel->reliable_channel_manager_api,
which also re-exports messaging_client_api). Deep emitters/listeners
(subscription_manager, waku_node, waku_node/relay, node_health_monitor,
recv_service, send_service) import the owning interface module directly.
kernel_api stays below node level (types/topics/message/store-common) so the
node->kernel_api imports are acyclic. liblogosdelivery builds.

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

logos_delivery/api/logos_delivery_api.nim

@@ -13,17 +13,16 @@ import results, chronos
 import brokers/event_broker
 import types as api_types
 
-# `EventConnectionStatusChange` lives in the decomposed health-events module.
-# Re-export it here so the orchestrator surfaces it without duplicating the type.
-import logos_delivery/waku/api/events/health_events as health_events
-
 export api_types, event_broker
-export health_events
 
 type
   ## Entry point. Holds one instance of each API layer.
   ILogosDelivery* = ref object of RootObj
 
+EventBroker:
+  type EventConnectionStatusChange* = object
+    connectionStatus*: ConnectionStatus
+
 method start*(self: ILogosDelivery): Future[Result[void, string]] {.async, base.} =
   return err("ILogosDelivery.start not implemented")
 

logos_delivery/waku/api/events/message_events.nim

@@ -1,10 +0,0 @@
-import brokers/event_broker
-import logos_delivery/api/types
-import logos_delivery/waku/[waku_core/message, waku_core/topics]
-export event_broker, types
-
-EventBroker:
-  # Internal event emitted when a message arrives from the network via any protocol
-  type MessageSeenEvent* = object
-    topic*: PubsubTopic
-    message*: WakuMessage