Add inline document mentions

[priethor]

What

Part of #160

Lets users mention Cortext documents with @ while editing, in both the page editor and the row detail editor. The autocomplete searches Cortext documents, inserts a compact inline mention, and keeps clicks inside the Cortext router. On public pages, readable mentions render as links with the current title and icon; private, deleted, or unreadable targets fall back to the saved label.

How

• Saving mentions as anchors with the target document id.
• Refreshing saved title/link snapshots when the target changes.
• Rendering public mentions through normal read permissions so private titles do not leak.

Testing Instructions

1. Open a Cortext document and type @ in a text block.
2. Pick another Cortext document from the autocomplete menu.
3. Save and reload the document, then confirm the mention still shows the right title and icon.
4. Rename the target document and confirm the mention updates in the source document.
5. Click the mention in the editor and confirm Cortext opens the target document.
6. Open the source document publicly and confirm the mention renders correctly.

Screen recording

Grabacion.de.pantalla.2026-06-26.a.las.14.27.17.mov