Make the workspace usable on mobile

## Goal

Cortext currently squeezes its desktop layout into narrow screens. The left navigation, row detail panel, and properties block compete for the same space, leaving too little room to read or edit content.

Give the workspace a proper mobile layout for navigating between documents and editing them.

## Tasks

- [ ] Turn the left sidebar into mobile navigation that overlays the content and can be reopened from the top bar.
- [ ] Close the mobile navigation after opening a page or collection.
- [ ] Review the row detail modes on narrow screens and implement a full-width mobile experience. The side peek should not share the screen with the collection.
- [ ] Adapt the document properties block for narrow screens, stacking labels and values where needed and keeping every control within the viewport.
- [ ] Check pages, full-page collections, and row detail views at common phone widths without changing their desktop behavior.

## Acceptance criteria

- The left navigation does not permanently take space away from the document on mobile.
- Opening a page or collection closes the navigation and shows the selected document.
- Opening a row provides a usable full-width detail surface with a clear way back.
- Properties can be read and edited without clipped controls, overlapping content, or horizontal page scrolling.
- The desktop workspace continues to behave as it does today.

Start by locating the workspace's left navigation, top bar, row detail modes, and document properties components, then run the app at common phone widths. Trace page, full-page collection, and row-detail navigation to verify the mobile transitions. Done means mobile views are usable without horizontal scrolling while desktop behavior remains unchanged.

Written by the indexing model from the issue text.