fix(streaming): commit EnvCell landblocks atomically (#214)

Carry one complete cell payload with each streaming completion and publish visibility, physics, and render state on the render thread. Remove the obsolete post-readiness login reload that triggered a duplicate dungeon build.

Co-Authored-By: Codex <noreply@openai.com>

src/AcDream.App/Rendering/PortalVisibilityBuilder.cs

@@ -188,7 +188,7 @@ public static class PortalVisibilityBuilder
                 // portal, the exact inputs the BFS guards read — BEFORE the guards run, so
                 // a portal the loop silently `continue`s past is still visible here. An
                 // empty OUTSIDEVIEW can then be traced to the precise gate: polyLen<3 (empty
-                // polygon from BuildLoadedCell), interiorSide=false (camera back-facing the
+                // polygon from EnvCellLandblockBuildBuilder), interiorSide=false (camera back-facing the
                 // portal — a legitimately-empty result, not a bug), or (if both OK) a
                 // downstream projection/clip failure shown by the EXIT-PROJ/EXIT-CLIP lines.
                 for (int ci = 0; ci < cameraCell.Portals.Count; ci++)