Phase 7 Task 7.1 final step. The `crate::document` module's shared
enum/value types were the last remnant of shell-core's dead `Document`
model. This repoints every consumer onto canonical types and deletes
the module entirely.
- Enum types (`Tool`, `AlignAction`, `FillType`, `FlexLayout`,
`PropertyTab`, `PropertyFocus`, `ColorTarget`, `Viewport`, `NodeId`,
`BooleanOp`, `ChatAnchor`, `ReorderDirection`) repointed onto their
variant-identical `op_editor_core` equivalents.
- `NodeKind` / `Effect` / `DropShadow` are paint-time scene types with
no canonical home — moved into `layout_scene.rs` (the surviving
scene type that is their only consumer). `Stroke` consumers switched
to the existing `SceneStroke`.
- `VariableTable` + friends (`Variable`, `ThemeAxis`, `ThemedValue`,
`VariableKind/Scalar/Value`) are a shell-core-local paint-time
aggregate consumed by the `LayoutScene` builder — moved to a new
crate-root `scene_vars` module.
- `editor_state_ext.rs` converters that became identity now that
widgets speak canonical types deleted (`doc_tool`, `doc_align_action`,
`doc_fill_type`, `doc_flex_layout`, `doc_property_tab`,
`doc_property_focus`). The widget-local→canonical reverse bridges
(`file_menu_choice`, `shape_choice`, `export_format`) added there.
- `op-pen-loader/bridge_enums_rev.rs` (the SC document→EC enum bridge)
deleted; hosts feed canonical widget hit-test results straight in.
- Dead `large_document_perf.rs` integration test (exercised the
removed `Document` struct directly) deleted.
Pure type-repointing — widgets/canvas/export paint identically.
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