feat(applications): restore the application custom settings tab (#23256)

## Summary

Restores the application **custom settings tab** feature that was
removed in #22156. This reverts that removal so applications can again
expose a custom settings tab via a front component.

## Changes

- Restore the `SettingsApplicationCustomTab` component and its tab
entry/rendering in `SettingsApplicationDetails`.
- `ApplicationManifestMigrationService` syncs
`settingsCustomTabFrontComponent` from application manifests again
(`syncDefaultRoleAndSettingsCustomTab`), resolving the front component
from `settingsCustomTabFrontComponentUniversalIdentifier`.
- Remove the deprecation annotations added by #22156:
- `ApplicationDTO.settingsCustomTabFrontComponentId` (drop GraphQL
`@deprecated`)
-
`ApplicationManifest.settingsCustomTabFrontComponentUniversalIdentifier`
- the `settingsCustomTabFrontComponentId` column comment on
`ApplicationEntity`
- Regenerate the corresponding GraphQL schema/types to drop the
`@deprecated` reason.

The DB column was never dropped, so no schema migration is required.


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Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-docs/developers/extend/apps/config/application.mdx

@@ -36,6 +36,7 @@ Notes:
 - Pre-install, post-install, and uninstall functions are detected automatically during the manifest build — you do not need to reference them in `defineApplication()`.
 - Passing `defaultRoleUniversalIdentifier` explicitly is still supported for backward compatibility, but is deprecated in favor of `defineApplicationRole()`.
 - `serverVariables` are instance-scoped configuration and secrets (e.g. API keys). Unlike `applicationVariables`, they declare no value in the manifest — the workspace operator fills them in from the app's settings, and they are injected into logic functions only once set.
+- To render a custom configuration UI inside the app's **Settings** tab (in place of the default variable configuration section), declare a front component with [`defineSettingsFrontComponent()`](/developers/extend/apps/layout/front-components#custom-settings-component) in its own file. Only one is allowed per app. System-managed sections (auto-upgrade, App URL, connections) always remain visible.
 
 ## Variable types