feat(net): Phase 4.8 — send GameAction.LoginComplete after EnterWorld

User reported that when they observed acdream's character through a
second AC client running on a different account, the character
rendered as a stationary purple haze (AC's "loading screen / portal
space" indicator) instead of a normal avatar. The character was
"in-world enough" to receive the CreateObject stream but never
"in-world enough" for the server to flip its first-enter-world flag,
push initial property updates / equipment overrides, or show the
character to other clients in the area.

Root cause: WorldSession.EnterWorld stopped after sending
CharacterEnterWorld (0xF657). The handshake is supposed to continue
with one more message — a GameAction(LoginComplete) — that ACE's
GameActionLoginComplete handler interprets as "client has exited
portal space, mark FirstEnterWorldDone, push property updates,
make the character visible to others."

Wire layout (confirmed via
references/ACE/Source/ACE.Server/Network/GameAction/GameActionPacket.cs
and .../Actions/GameActionLoginComplete.cs):

  u32 game-message opcode = 0xF7B1 (GameAction)
  u32 sequence            = 0  (ACE ignores; TODO comment in source)
  u32 GameActionType opc  = 0x000000A1  (LoginComplete)

Send happens immediately after CharacterEnterWorld and just before
flipping the WorldSession state to InWorld. acdream has no portal-
space transition animation, so we can claim "loading complete" the
moment we've sent the EnterWorld message — the dat-side world is
already loaded by then.

1 new test (97 Core.Net total). 220 tests green overall.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/WorldSession.cs

@@ -201,6 +201,15 @@ public sealed class WorldSession : IDisposable
         if (!serverReady) { Transition(State.Failed); throw new TimeoutException("ServerReady not received"); }
 
         SendGameMessage(CharacterEnterWorld.BuildEnterWorldBody(chosen.Id, account));
+
+        // Tell the server "I'm done loading, you can show me to other players
+        // and push my initial property updates." Without this, the character
+        // stays in a transitional state and renders as the purple loading
+        // haze to other clients in the same area. ACE's GameActionLoginComplete
+        // handler is what flips Player.FirstEnterWorldDone and triggers
+        // SendPropertyUpdatesAndOverrides.
+        SendGameMessage(GameActionLoginComplete.Build());
+
         Transition(State.InWorld);
     }