chore(O-T1): create Core/Rendering/Wb directory + NOTICE.md attribution

Phase O setup: extracted-WB code home + MIT attribution per O-D5.
Spec: docs/superpowers/specs/2026-05-21-phase-o-dat-path-unification-design.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

NOTICE.md

@@ -0,0 +1,45 @@
+# Third-Party Notices
+
+This file lists third-party software used by acdream, along with their
+license terms and copyright notices.
+
+---
+
+## WorldBuilder
+
+Portions of acdream's rendering and dat-handling code are copied from
+WorldBuilder (https://github.com/Chorizite/WorldBuilder), MIT-licensed.
+The extracted code lives under:
+
+- `src/AcDream.Core/Rendering/Wb/` — pure helpers (texture decode,
+  scenery transforms, terrain math).
+- `src/AcDream.App/Rendering/Wb/` — GL infrastructure and mesh pipeline.
+
+Original copyright holders: Chorizite contributors (see WorldBuilder's
+LICENSE file). Adapted by acdream maintainers to consume our
+`DatCollection` directly (replacing WB's `DefaultDatReaderWriter`) and
+to remove editor-only code paths.
+
+Original MIT license text:
+
+MIT License
+
+Copyright (c) Chorizite contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.