* refactor(editor): separate canvas view state
- Classify shared and view-local editor state explicitly
- Let canvas surfaces render supplied view state and report their viewport
- Preserve the existing one-canvas behavior by default
* fix(canvas): preserve loading render state
* refactor(editor): group state ownership modules
- Move shared and view state into the editor state namespace
- Model the partition with explicit interfaces and default factories
- Derive runtime view keys from the default view object
