refactor: unify layout customization mode (record pages + navigation) (#18640)

### What

Unifies record page layout editing and navigation menu editing into a
single global "layout customization" session. Dashboard editing stays
separate.

  ### How it works

  **Two edit mode systems, one context-based read:**
- `isLayoutCustomizationModeEnabledState` -- global atom for record
pages + navigation
- `isDashboardInEditModeComponentState` -- dashboard-only, independent
per-component atom
- `PageLayoutEditModeProvider` -- context that dispatches to
`RecordPageLayoutEditModeProvider` (reads global atom) or
`DashboardPageLayoutEditModeProvider` (reads component atom), one
component per file

  **Session registry + independent atoms:**
- `activeCustomizationPageLayoutIdsState` -- accumulates page layout IDs
as user navigates during customization (`string[]`)
- Save/cancel iterate the ID list and read each layout's draft/persisted
atoms independently
- Follows the same pattern as `settingsRoleIdsState` +
`settingsDraftRoleFamilyState`

  **Unified UI:**
- `LayoutCustomizationBar` replaces the old `NavigationMenuEditModeBar`
- Enter once -- edit record layouts + navigation -- save/cancel
everything together
- `useSaveLayoutCustomization` orchestrates sequential save: navigation
draft -- page layouts -- field widget groups
- Error snackbar on partial save failure (with TODO for future atomic
server mutation)

  **Draft protection during customization:**
- `PageLayoutRelationWidgetsSyncEffect` guarded -- only updates
persisted state from server, skips draft/currentLayouts while
customization is active
- `useExecuteTasksOnAnyLocationChange` skips draft reset when
customization mode is enabled
  - Command execution blocked during layout customization

  ### Cleanup
- Deleted `NavigationMenuEditModeBar`,
`isNavigationMenuInEditModeState`,
`isPageLayoutInEditModeComponentState`,
`useIsGlobalLayoutCustomizationActive`
- `DraftPageLayout` type changed from `Omit` to `Pick` (explicit fields)
- Removed save/cancel from `DefaultRecordCommandMenuItemsConfig` (bar
handles it now)
  - Extracted `useSaveFieldsWidgetGroups` from save orchestration
- Split `PageLayoutEditModeProvider` into 3 separate files (one
component per file, Twenty convention)

  ### Known issues
- **Stale deleted widget after save (pre-existing on `main`)**: Delete
widget -- save -- exit customization -- Apollo cache stale -- sync
effect overwrites Jotai from stale data -- widget reappears until
refresh. Separate PR needed, likely tied to the planned server-side
`saveLayoutCustomization` atomic endpoint.

  ### Open questions
- **Module location**: Layout customization hooks/states live in `/app`
-- should they move to their own `modules/layout-customization/`?
- **Atomic server mutation**: All save mutations are on metadata schema
(`createNavigationMenuItem`, `deleteNavigationMenuItem`,
`updateNavigationMenuItem`, `updatePageLayoutWithTabsAndWidgets`,
`upsertFieldsWidget`). A single `saveLayoutCustomization` endpoint could
make saves truly atomic.


https://github.com/user-attachments/assets/036ef542-97f3-485b-a68f-3726002c81fb

packages/twenty-front/src/modules/layout-customization/hooks/useEnterLayoutCustomizationMode.ts

@@ -0,0 +1,35 @@
+import { activeCustomizationPageLayoutIdsState } from '@/layout-customization/states/activeCustomizationPageLayoutIdsState';
+import { isLayoutCustomizationModeEnabledState } from '@/layout-customization/states/isLayoutCustomizationModeEnabledState';
+import { filterWorkspaceNavigationMenuItems } from '@/navigation-menu-item/common/utils/filterWorkspaceNavigationMenuItems';
+import { navigationMenuItemsDraftState } from '@/navigation-menu-item/common/states/navigationMenuItemsDraftState';
+import { navigationMenuItemsSelector } from '@/navigation-menu-item/common/states/navigationMenuItemsSelector';
+import { useStore } from 'jotai';
+import { useCallback } from 'react';
+
+export const useEnterLayoutCustomizationMode = () => {
+  const store = useStore();
+
+  const enterLayoutCustomizationMode = useCallback(() => {
+    const isLayoutCustomizationModeAlreadyEnabled = store.get(
+      isLayoutCustomizationModeEnabledState.atom,
+    );
+
+    if (isLayoutCustomizationModeAlreadyEnabled) {
+      return;
+    }
+
+    const prefetchNavigationMenuItems = store.get(
+      navigationMenuItemsSelector.atom,
+    );
+    const workspaceNavigationMenuItems = filterWorkspaceNavigationMenuItems(
+      prefetchNavigationMenuItems,
+    );
+    store.set(navigationMenuItemsDraftState.atom, workspaceNavigationMenuItems);
+
+    store.set(activeCustomizationPageLayoutIdsState.atom, []);
+
+    store.set(isLayoutCustomizationModeEnabledState.atom, true);
+  }, [store]);
+
+  return { enterLayoutCustomizationMode };
+};