Make page layout tab layoutMode diffable and default standalone pages to vertical list (#23596)

Reported on Discord: an app declared a `STANDALONE_PAGE` layout with one
`FRONT_COMPONENT` widget and got a small bordered card instead of a
full-bleed page, and setting `layoutMode` afterwards changed nothing.

Two bugs:

- `pageLayoutTab.layoutMode` was `toCompare: false`, so it was written
once at create and never diffed again. Changing it in a manifest and
redeploying was a silent no-op, and `updatePageLayoutTab(layoutMode:)`
was accepted by the API then dropped by the runner's update sanitizer.
- A manifest tab that omits `layoutMode` defaulted to `GRID` regardless
of page layout type, and a `GRID` tab always renders its widgets as
cards on a 12-column grid. Standalone pages now default to
`VERTICAL_LIST`, where a lone widget owns the tab.

Also fixes the SDK scaffolder (`twenty add page-layout` emitted a tab
with no `position`, which does not typecheck) and the docs claim that a
single widget is always full-bleed.

Worth knowing for review: this does not migrate workspaces holding
legacy `CANVAS` tabs. The standard-app sync only runs against a fresh
schema, so those rows stay `CANVAS` and keep rendering correctly through
the derived presentation.


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packages/twenty-server/src/engine/metadata-modules/flat-entity/constant/__tests__/__snapshots__/all-universal-flat-entity-properties-to-compare-and-stringify.constant.spec.ts.snap

@@ -213,6 +213,7 @@ exports[`ALL_UNIVERSAL_FLAT_ENTITY_PROPERTIES_TO_COMPARE_AND_STRINGIFY should ma
       "position",
       "deletedAt",
       "icon",
+      "layoutMode",
       "isActive",
       "overrides",
     ],

packages/twenty-server/src/engine/metadata-modules/flat-entity/constant/all-entity-properties-configuration-by-metadata-name.constant.ts

@@ -1116,7 +1116,7 @@ export const ALL_ENTITY_PROPERTIES_CONFIGURATION_BY_METADATA_NAME = {
       universalProperty: 'pageLayoutUniversalIdentifier',
     },
     layoutMode: {
-      toCompare: false,
+      toCompare: true,
       toStringify: false,
       universalProperty: undefined,
     },