[rubenvdlinde]

Part of #3099, on top of #3211 (start page autofill). This is the model and the server side of a tabs widget: a widget whose tabs each hold widgets of their own. The UI comes in #3217.

@enjeck, this is the only pull request in the stack that changes the model of #3100: tables_contexts_widget gets parent_id and parent_tab. Do you agree with that model for widgets in tabs? If you'd rather keep #3100 as it is, this pull request and #3217 can be dropped without affecting the others.

Size: 333 lines: 229 code, 83 tests and 21 generated OpenAPI (in a separate commit).

What changes

• A tabs widget type on the server (GridWidgetTypes): its tabs setting names the tabs, one per line, at most 20.
• The model: tables_contexts_widget gets parent_id (the tabs widget) and parent_tab (the position of the tab), both nullable, in their own migration Version2500Date20261030010000. The app version goes to 2.5.0-dev.2, one dev step from feat(pages): fill the start page of an application with widgets #3211.
• Saving a page takes parentIndex (the position of the tabs widget in widgets) and parentTab for a widget in a tab; page responses carry parentId and parentTab. The server checks that the parent is a tabs widget of the same page that sits on the page itself, so tabs go one level deep and a tabs widget never sits in a tab, and that the tab exists. The cap of 100 widgets counts the widgets in tabs too.
• Moving a user's data keeps widgets in their tabs; a widget whose tabs widget or tab didn't come along is skipped with a warning.

Until #3217, the frontend from #3214 on doesn't offer the tabs type, because it only offers types it can show.

How it was tested

On Nextcloud 34 with PostgreSQL:

• PageServiceTest: a widget in a tab listed before its tabs widget is saved with its parent; 400 for a tab without tabs widget, a parent that isn't a tabs widget, a parentIndex that isn't a number, tabs in tabs, an unknown tab and more than 20 tabs (one data provider)
• WidgetServiceTest (database): putting a widget in a tab and taking it out again
• ContextPagesRoundTripTest (database): widgets in tabs survive a user data import, an orphan is skipped
• the full unit suite on PostgreSQL and SQLite: 571 tests each
• composer run rector:check, php -l, composer cs:check and psalm, all clean
• no frontend changes besides the regenerated types

🖼️ Screenshots

No UI change; #3217 has the screenshots.

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔙 Backport requests are created or not needed: /backport to stableX.X
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI