fix(app): scale order for live entities + FlyCamera speed tune (Phase 5c-fix)

User-reported visuals after Phase 5c ObjScale landed:
  - Nullified Statue is bigger but "distorted" and half-sunken into the
    foundry
  - WASD/Space/Ctrl camera speed too fast

Fixes:

1. Scale multiplication order. Phase 5c used `scaleMat * PartTransform`,
   which in C# row-vector Matrix4x4 semantics means "scale first (in
   mesh-local space), then apply PartTransform." For multi-part meshes
   where each part has an attachment translation, this scales the mesh
   but leaves the attachment offset un-scaled — so child parts drift
   relative to each other and the base anchor ends up below the ground.
   Offline scenery hydration has always used the opposite order:
   `PartTransform * scaleMat`, meaning "transform first, then scale the
   resulting position." Matching that order fixes both distortion and
   sinking in one change, and makes live entities consistent with
   scenery's proven path.

2. FlyCamera.MoveSpeed 100 → 35. 100 world units/sec is ~half a landblock
   per second at AC scale — fine for terrain-scouting but too aggressive
   for inspecting specific entities like the foundry statue. 35 is a
   little faster than walk pace and feels right for visual iteration.

src/AcDream.App/Rendering/FlyCamera.cs

@@ -11,7 +11,7 @@ public sealed class FlyCamera : ICamera
     public float FovY { get; set; } = MathF.PI / 3f;
     public float Aspect { get; set; } = 16f / 9f;
 
-    public float MoveSpeed { get; set; } = 100f;         // world units per second
+    public float MoveSpeed { get; set; } = 35f;          // world units per second (AC cell size = 24)
     public float MouseSensitivity { get; set; } = 0.003f;
 
     private const float PitchLimit = 1.5533f;  // ~89 degrees