[mostafasadeghidev]

Split out of #501, per review: select-all alone, on main.

What

• Ctrl/Cmd+A selects every asset the grid shows; pressed again with everything selected, it clears the selection.
• A toolbar All button does the same and makes the shortcut discoverable (Select all N items / Clear selection).

Why

Emptying the trash or tagging a folder's worth of uploads meant clicking every file.

Behaviour worth reviewing

• "All" is visibleAssets — what the folder, filter and search show — never the whole library, so "select all, then delete" in the trash can't reach a live file that isn't on screen.
• The shortcut is document-level (the grid has no tabindex). It stands down in a text field, where the browser's own select-all is meant, and while a real modal is open.
• It keys on aria-modal="true", not role="dialog". Selecting one asset opens the viewer window, which carries the role but deliberately leaves the grid usable; keying on the role disabled the shortcut almost everywhere in Media.

Tests

selectAll.test.tsx renders MediaCanvas and presses the real shortcut and button — no copies of the logic. Each guard was checked by removing it from the component: keying on role="dialog", selecting the whole library, ignoring the search box — each turns the suite red.

Verification

bunx tsc -b                         clean
bunx eslint src/admin/pages/media   clean
bun test src/__tests__/media        all pass

Docs: one line in docs/features/media.md.