chore(architecture): enforce layer boundaries

editor/AGENTS.md

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+# Editor State Rules
+
+- `editor/` owns transient app/editor state types and the app store.
+- Transient state includes viewport/camera, selection, tools, active entities, and drag/session state.
+- Do not put persisted document fields here; use `core/` for saved image document state.
+- Do not import React, renderer/WebGL, storage, network, or filesystem APIs.
+- The store must expose read/subscribe and command dispatch only; no public direct setters.
+- State changes must flow through commands, including viewport/camera changes.