feat(contexts): edit the menu when creating an application

[remko48]

The create application dialog gets a menu editor, so an application can be created with its menu in one go.

What changes

• MenuItemsEditor: an ordered list of menu items. Each item has an icon, a label and what it opens: a view, a page with widgets, a table or an external link. Only tables and views the user can manage are offered, since the server adds them to the application as resources. Picking a view or table fills in an empty label.
• Ordering and nesting: entries can be dragged by their handle, and every entry has move up/down buttons plus an indent button (top-level entries) or an outdent button (child entries), so the menu can be arranged with the keyboard. A parent moves together with its children; an entry with children cannot be indented; removing a parent moves its children to the top level instead of deleting them.
• Validation: the editor checks every entry with the same rules as the server (label, target, http/https link). Errors show once a row is left, and all of them on submit; an invalid menu blocks creating the application.
• ApplicationIcon: shows a material icon by name, used for the menu item icons.
• menuItems.js: the list operations of the editor, and turning its list into the API payload, including parentIndex for nested items.
• CreateContext: sends the menu with the new application.
• Deleting an application (existing behaviour on main, not caused by this stack): the delete removes the application first, inside a transaction that is retried, so it holds the write lock before it reads. On SQLite a delete that read first failed at once when another request wrote meanwhile.
• Tests: a Cypress component test covers the list operations, and a unit test covers the delete order.

Page target

Dashboard item is removable (nextcloud#3099)

The create dialog shows the dashboard item first. It is an ordinary item: you can rename it, give it an icon, move it, nest it and remove it, and other items can go above it. Only what it opens is fixed. The server stores the menu as submitted, so a removed dashboard item stays removed. It is sent as {targetType: 'page', targetId: null, technicalName: 'dashboard', label}, and the server resolves it to the new start page. A page item from the API passes through menuItems.js unchanged, without a validation error.

Tests:

• npm run test:component -- --spec cypress/component/menuItems.cy.js: 13 passing.
• New playwright/e2e/context-menu.spec.ts: creates an application in the UI and checks that the dashboard item comes first, renames it and moves a link above it, that the saved menu is the link then Overview -> page <start page id>, and that the application opens on its start page; a second test removes the item in the dialog and checks the saved menu is empty and the application still opens. 2 passed at 1600px.
• context.spec.ts and context-navigation.spec.ts: 8 passed. One test needs the CI timeout of 120 s on the local instance.

The menu is not shown in the UI yet, so the check opens the start page by route. Prepared in the Conduction fork for porting upstream by @remko48. Prepared with Claude Code.

🖼️ Screenshots

🏚️ Before	🏡 After

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🏁 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
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🤖 AI (if applicable)

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