feat(applications): standalone application shell with its own menu

[rubenvdlinde]

Rebuild of #39 (originally #25) on the page model of nextcloud#3100 / nextcloud#3099 (#46-#51), see #13. Stacked on stack-5-main (the page stack #46-#51 with the menu stack #20-#23 merged in; the dashboard menu item and the start page share the technical name dashboard).

What changes

An application opened on its own, at /apps/tables/app/{id}, gets its own navigation: its menu replaces the Tables navigation, and every menu item opens inside the application.

• ApplicationNavigation: the application's icon, name and description, then its menu, nested one level like the stored menu. A link opens outside the app. The owner gets "Configure in Tables".
• Menu item route /application/{id}/menu/{technicalName}: a page item opens that page; the dashboard item opens the start page with its widgets and its tables and views, any other page opens as a grid page. A view or table item shows its rows (DataWidget, the component of a data widget). An unknown or broken item shows an empty state.
• First page: opened on its own, the application starts on its first menu item that is not a link. For a new application that is the dashboard item.
• Start page entry: when no menu item opens the start page (applications created before the menu, or a removed dashboard item), the navigation gets an entry for it, titled by the page title or "Dashboard".
• Inside Tables: a menu item route shows a breadcrumb back to the application and an "Open application" button.
• MenuItemIcon: a warning icon for a broken item, else the chosen icon, else one for what the item opens.
• Focus: the content area only takes focus after a first click or key press, so no focus ring is drawn on load.

What changed because of nextcloud#3100 / nextcloud#3099

• feat(applications): standalone application shell with its own menu #39 rendered every page, the start page included, as a grid. On Grid pages in applications (data model and API) nextcloud/tables#3100 the start page keeps its tables and views (page_content) and shows its widgets above them (feat(pages): widgets on the application start page (step 6, separable) #51), so the dashboard item renders exactly that, the same as the start page inside Tables.
• Opened on its own, the application header and the page bar of feat(pages): grid pages in the application UI (#3099, step 4) #49 are hidden: Grid pages in applications (frontend) nextcloud/tables#3099 makes the page bar the design surface inside Tables and the menu the navigation of the standalone app. Inside Tables nothing changes on /application/{id}.
• Pages are looked up in the context response's pages (title, emoji, page type from feat(pages): store grid pages and their widgets relationally (#3100, step 1) #46) instead of a separate page list.

Tests

Nextcloud 34 container (PostgreSQL 16), Playwright at 1600 x 1000, --timeout=120000:

• playwright/e2e/application.spec.ts (ported from feat(applications): standalone application shell with its own menu #39): opened on its own, the menu shows 4 items and starts on /menu/dashboard with the start page's header widget and table and no page bar; a page item opens its grid page; a table item its rows; a link keeps its URL; no focus on load. Inside Tables the breadcrumb and "Open application". A page item whose page was deleted shows the warning icon and the empty state. Without a dashboard item the start page gets its own entry. 4 passed (27.9s).
• context-grid-pages.spec.ts, context-menu.spec.ts, context.spec.ts, context-navigation.spec.ts: 17 passed (6.5m).
• env -u ELECTRON_RUN_AS_NODE npx cypress run --component --spec cypress/component/menuItems.cy.js: All specs passed! 15 15 (menu routes, menu tree).
• npm run lint: 0 errors, 1 inherited warning (src/store/store.js:176); npm run stylelint: clean; npm run build: OK.
• stack-5-main itself: whole unit suite OK (517 tests, 1077 assertions), composer cs:check no files, psalm No errors found!.

Inherited: the create endpoint answers with pages[].pageType while the read endpoint uses page_type; the spec reads the start page id from the dashboard menu item.

Prepared in the Conduction fork for porting upstream by @remko48. Prepared with Claude Code.