fix(ui): open folder items in new tab on CMD/Shift+double-click

[amateurbeekeeper]

What I did

Fixes #15837

When navigating the folder view, holding CMD or Shift while double-clicking a file card or table row now opens the item in a new browser tab.

Root cause

Two things were broken:

1. No new-tab support in navigateAfterSelection — navigation always went through router.push(), which navigates in-place. Folder cards and draggable table rows are div/tr elements with pointer event handlers, not <a> tags, so the browser's native new-tab behaviour never fired.

2. Modifier-key double-click was undetectable — the double-click check only ran in the else branch (normal click), after the isCtrlPressed/isShiftPressed checks. So CMD/Shift+double-click was intercepted for multi-selection before double-click detection ever ran. Also, the previous detection used dragOverlayItem as a proxy for "last clicked item", but dragOverlayItem isn't reliably set during modifier-key clicks.

Fix

providers/Folders/index.tsx

1. Add a lastClickItemKey ref to reliably track the last-clicked item, independent of dragOverlayItem.
2. Move double-click detection to before the modifier-key branches, so CMD/Shift+double-click is caught first.
3. Add newTab?: boolean to navigateAfterSelection — when true, calls window.open(url, '_blank') instead of router.push().

Behaviour

Action	Before	After
Single click	select item	select item (unchanged)
Double click	navigate in same tab	navigate in same tab (unchanged)
CMD/Shift + single click	multi-select	multi-select (unchanged)
CMD/Shift + double click	multi-select (broken)	open in new tab ✓

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