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/workspace-manager/dev-seeder/core/utils/seed-feature-flags.util.ts

@@ -45,16 +45,6 @@ export const seedFeatureFlags = async ({
         workspaceId: workspaceId,
         value: true,
       },
-      {
-        key: FeatureFlagKey.IS_NAVIGATION_MENU_ITEM_ENABLED,
-        workspaceId: workspaceId,
-        value: true,
-      },
-      {
-        key: FeatureFlagKey.IS_NAVIGATION_MENU_ITEM_EDITING_ENABLED,
-        workspaceId: workspaceId,
-        value: true,
-      },
       {
         key: FeatureFlagKey.IS_MARKETPLACE_ENABLED,
         workspaceId: workspaceId,