fix(core+app): Phase B.3 — Setup.StepUpHeight + scenery road exclusion

Four targeted fixes for user-reported movement/visual bugs:

1. Player entity disappearing: GpuWorldState now supports persistent
   entities (MarkPersistent/DrainRescued). The player character survives
   landblock unloads and gets re-injected into the streaming window at
   the current center landblock.

2. Feet sinking into terrain: +0.15 Z bias in PlayerMovementController
   keeps the character model above terrain z-fighting edge cases.

3. Camera after portal teleport: ChaseCamera.Update now called
   immediately after teleport snap so the camera recenters on the new
   position instead of lingering at the pre-teleport location.

4. Scenery on roads: SceneryGenerator now checks road status at the
   final displaced position (not just the origin vertex), catching
   objects that drift from non-road vertices onto road cells.

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

src/AcDream.App/Streaming/GpuWorldState.cs

@@ -48,6 +48,13 @@ public sealed class GpuWorldState
     /// </summary>
     private readonly Dictionary<uint, List<WorldEntity>> _pendingByLandblock = new();
 
+    /// <summary>
+    /// Entities that must survive landblock unloads (e.g. the player character).
+    /// On RemoveLandblock, these are rescued and re-parked as pending for their
+    /// current canonical landblock.
+    /// </summary>
+    private readonly HashSet<uint> _persistentGuids = new();
+
     // Cached flat view over all entities across all loaded landblocks,
     // rebuilt on each add/remove. The renderer holds a reference to this
     // list, so rebuilding it replaces the reference atomically.
@@ -112,12 +119,27 @@ public sealed class GpuWorldState
         RebuildFlatView();
     }
 
+    /// <summary>
+    /// Mark a server-GUID as persistent — this entity survives landblock unloads
+    /// and gets re-parked as pending for its current canonical landblock.
+    /// </summary>
+    public void MarkPersistent(uint serverGuid) => _persistentGuids.Add(serverGuid);
+
     public void RemoveLandblock(uint landblockId)
     {
-        // Drop pending entries for the same landblock — if the landblock
-        // is being unloaded the player has moved away from it, and any
-        // pending spawns that arrived for it are no longer relevant. The
-        // server will resend them via CreateObject when the player returns.
+        // Rescue persistent entities before removal. These get appended
+        // to the _persistentRescued list; the caller is responsible for
+        // re-injecting them (via AppendLiveEntity) into whatever landblock
+        // the player is currently on.
+        if (_loaded.TryGetValue(landblockId, out var lb))
+        {
+            foreach (var entity in lb.Entities)
+            {
+                if (_persistentGuids.Contains(entity.Id))
+                    _persistentRescued.Add(entity);
+            }
+        }
+
         _pendingByLandblock.Remove(landblockId);
         _aabbs.Remove(landblockId);
 
@@ -125,6 +147,20 @@ public sealed class GpuWorldState
             RebuildFlatView();
     }
 
+    private readonly List<WorldEntity> _persistentRescued = new();
+
+    /// <summary>
+    /// Drain entities rescued from unloaded landblocks. The caller should
+    /// re-inject each via <see cref="AppendLiveEntity"/> with its current position.
+    /// </summary>
+    public List<WorldEntity> DrainRescued()
+    {
+        if (_persistentRescued.Count == 0) return _persistentRescued;
+        var result = new List<WorldEntity>(_persistentRescued);
+        _persistentRescued.Clear();
+        return result;
+    }
+
     /// <summary>
     /// Append an entity to a specific landblock's slot. Used by the live
     /// CreateObject path where the server spawns entities at a server-side