fix(streaming): #145 — teleport re-use via server-authoritative placement

Portals only worked once per session: teleporting OUT of a dungeon
mis-rooted the player into the SOURCE dungeon's coordinate frame, so every
move was sent dungeon-framed and ACE rejected it ("failed transition") —
the player couldn't move, never reached a portal, and the world wouldn't
re-render (only skybox).

Root cause: acdream's streaming-relative frame recenters on teleport, but
resident physics landblocks keep their load-time world-offset. After
recentering onto the outdoor destination, the collapsed source dungeon
(offset 0,0 as the prior center) and the destination (offset 0,0 as the
new center) overlap, and the Z-agnostic outdoor cell-snap returns the
dungeon for both the arrival placement and every per-frame resolve.

Fix (server-authoritative teleport placement):
- Drop the stale source center landblock from physics at the teleport
  recenter (GameWindow.OnLivePositionUpdated) so the resolve falls through
  to the server position (Resolve NO-LANDBLOCK verbatim) until the
  destination streams in.
- Place outdoor teleports immediately (TeleportArrivalRules) — holding is
  futile because streaming does not progress during a PortalSpace hold.
- Clear a dangling CellGraph.CurrCell when its landblock is removed
  (PhysicsEngine.RemoveLandblock) — otherwise the dungeon-streaming gate
  keeps streaming collapsed onto the gone dungeon (only skybox renders).

Keeps DungeonStreamingGate (gate suppression during the hold). Indoor
(dungeon-entry) placement is unchanged (cell-keyed, IsSpawnCellReady).

User-verified: in->out->re-enter works repeatedly, no ACE errors, world
renders. Remaining facets (server objects + own avatar not rendering after
a teleport-out) are entity render/lifecycle — split to #138.

Registers AP-36 + AD-2 updated. New: DungeonStreamingGate (+4 tests),
TeleportArrivalRules (+4 tests). Build + 2727 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Streaming/StreamingController.cs

@@ -215,6 +215,8 @@ public sealed class StreamingController
     /// </summary>
     private void EnterDungeonCollapse(int cx, int cy, uint centerId)
     {
+        if (!_collapsed || _collapsedCenter != centerId)
+            Console.WriteLine($"streaming: dungeon collapse -> 0x{centerId:X8}");
         _collapsed = true;
         _collapsedCenter = centerId;
         _clearPendingLoads?.Invoke();
@@ -263,6 +265,9 @@ public sealed class StreamingController
     /// </summary>
     private void ExitDungeonExpand(int observerCx, int observerCy)
     {
+        Console.WriteLine(
+            $"streaming: dungeon EXIT-expand -> ({observerCx},{observerCy}) " +
+            $"(was collapsed on 0x{_collapsedCenter:X8})");
         _collapsed = false;
         var rebuilt = new StreamingRegion(observerCx, observerCy, NearRadius, FarRadius);