feat(B.5): pickup feedback chat line + toast ("You pick up the X.")

After B.5 shipped, the actual pickup was invisible feedback-wise: the
item left the ground, ACE despawned it via PickupEvent (0xF74A), and
the ItemRepository got updated — but the player had no visual
acknowledgement that anything happened. The M1 demo's "pick up an
item" target visually felt like the item just vanished into the void.

Add a new EntityPickedUp event to WorldSession that fires from the
PickupEvent (0xF74A) dispatch branch BEFORE EntityDeleted, so the
subscriber can still read the entity's display name from
_entitiesByServerGuid before the despawn handler clears it.

GameWindow subscribes during the live-session wiring block and emits
a retail-style system chat line plus a debug toast on every successful
pickup, mirroring retail behavior (retail synthesized this line
client-side; ACE doesn't echo it).

Closes the M1 demo "pick up" target's visible-payoff gap.

src/AcDream.App/Rendering/GameWindow.cs

@@ -1921,6 +1921,17 @@ public sealed class GameWindow : IDisposable
             _liveSession.PlayerKilledReceived += pk =>
                 Chat.OnPlayerKilled(pk.DeathMessage, pk.VictimGuid, pk.KillerGuid);
 
+            // B.5 polish (2026-05-14): surface successful pickups as a
+            // retail-style "You pick up the X." system chat line plus a
+            // toast. PickupEvent fires BEFORE the EntityDeleted despawn
+            // chain so the entity-name lookup still hits.
+            _liveSession.EntityPickedUp += parsed =>
+            {
+                string name = DescribeLiveEntity(parsed.Guid);
+                Chat.OnSystemMessage($"You pick up the {name}.", chatType: 0);
+                _debugVm?.AddToast($"Picked up: {name}");
+            };
+
             _liveSession.TurbineChatReceived += parsed =>
             {
                 if (parsed.Body is AcDream.Core.Net.Messages.TurbineChat.Payload.EventSendToRoom ev)

src/AcDream.Core.Net/WorldSession.cs

@@ -84,6 +84,17 @@ public sealed class WorldSession : IDisposable
     /// </summary>
     public event Action<DeleteObject.Parsed>? EntityDeleted;
 
+    /// <summary>
+    /// Fires when the session parses a 0xF74A PickupEvent game message —
+    /// distinguishes a despawn caused by a player pickup from a generic
+    /// <c>DeleteObject</c> despawn. Fires BEFORE <see cref="EntityDeleted"/>
+    /// for the same guid so subscribers can read entity state (e.g. name)
+    /// before the despawn handler removes the entity. Useful for "You pick
+    /// up the <i>X</i>" chat/toast feedback that needs the entity's display
+    /// name at the moment of pickup.
+    /// </summary>
+    public event Action<PickupEvent.Parsed>? EntityPickedUp;
+
     /// <summary>
     /// Payload for <see cref="MotionUpdated"/>: the server guid of the entity
     /// whose motion changed and its new server-side stance + forward command.
@@ -717,13 +728,21 @@ public sealed class WorldSession : IDisposable
                 // ACE sends PickupEvent (0xF74A) instead of DeleteObject
                 // when a player picks up a world item (Player_Tracking
                 // .RemoveTrackedObject with fromPickup=true). Downstream
-                // view-removal semantics are identical, so we adapt to
+                // view-removal semantics are identical to DeleteObject, so
-                // DeleteObject.Parsed and reuse the existing handler.
+                // we adapt to DeleteObject.Parsed and reuse the existing
+                // EntityDeleted handler. We also fire a distinct
+                // EntityPickedUp event BEFORE the despawn so a subscriber
+                // can read entity-side state (e.g. its display name) for
+                // pickup-feedback chat / toast lines while the entity is
+                // still resident.
                 var parsed = PickupEvent.TryParse(body);
                 if (parsed is not null)
+                {
+                    EntityPickedUp?.Invoke(parsed.Value);
                     EntityDeleted?.Invoke(
                         new DeleteObject.Parsed(
                             parsed.Value.Guid, parsed.Value.InstanceSequence));
+                }
             }
             else if (op == UpdateMotion.Opcode)
             {