chore: remove 1-19 upgrade commands and navigation menu item feature flags (#19083)

## Summary
- Deletes the entire `1-19` upgrade version command directory (7 files,
~1500 lines) and removes all references from the upgrade module and
command runner.
- Removes `IS_NAVIGATION_MENU_ITEM_ENABLED` and
`IS_NAVIGATION_MENU_ITEM_EDITING_ENABLED` feature flags from the enum,
seed data, generated schema files, and test mocks. These flags had no
remaining feature-gated code — navigation menu items are now always
enabled.

packages/twenty-server/src/engine/twenty-orm/entity-manager/workspace-entity-manager.spec.ts

@@ -239,8 +239,6 @@ describe('WorkspaceEntityManager', () => {
         IS_EMAILING_DOMAIN_ENABLED: false,
         IS_JUNCTION_RELATIONS_ENABLED: false,
         IS_COMMAND_MENU_ITEM_ENABLED: false,
-        IS_NAVIGATION_MENU_ITEM_ENABLED: false,
-        IS_NAVIGATION_MENU_ITEM_EDITING_ENABLED: false,
         IS_DRAFT_EMAIL_ENABLED: false,
         IS_USAGE_ANALYTICS_ENABLED: false,
         IS_RICH_TEXT_V1_MIGRATED: false,