Add support for standalone pages: a new `PageLayout` type
(`STANDALONE_PAGE`) that can be rendered independently at
`/page/:pageLayoutId`, not tied to any record or object context.
- New `STANDALONE_PAGE` page layout type
- New `PAGE_LAYOUT` navigation menu item type: adds a `pageLayoutId`
foreign key to `NavigationMenuItemEntity`, allowing sidebar items to
link directly to standalone pages
- New `GLOBAL_OBJECT_CONTEXT` command menu availability type: separates
object-context-dependent commands (Create Record, Import, Export, See
Deleted, Create View, Hide Deleted) from truly global ones, so
standalone pages only show relevant commands
- Frontend routing & rendering: adds a `/page/:pageLayoutId` route with
its own page component, header, and command menu
- Widget rendering refactor
- Instance commands: two fast 1.22 migrations: `pageLayoutId` column +
`STANDALONE_PAGE` enum, and `GLOBAL_OBJECT_CONTEXT` availability type
enum
- Workspace command: backfills existing command menu items from `GLOBAL`
to `GLOBAL_OBJECT_CONTEXT` where appropriate
- Dev seeds: adds a sample "Star History" standalone page with an iframe
widget for local development
