fix(file-tree): long-press opens the row context menu on touch devices

The three ContextMenuTrigger wrappers around FileTreeFile,
FileTreeFolder, and the RootDropFolder root-drop menu rendered as bare
<span> elements. HTML parser rules disallow <span> from containing <div>
children, so the row div ended up as the span's sibling and Radix's
pointerdown / contextmenu handlers — and its WebkitTouchCallout: none
style — never reached the actual row.

Effect on touch:
* iOS Safari showed its native long-press callout (Copy / Share / Save
  Image), eating the gesture before Radix's 700ms long-press timer could
  open the menu.
* Android Chrome and desktop touchscreens likewise had no path to open
  the per-row menu.

Desktop right-click worked because onContextMenu propagates by capture
and bubble independently of the parent-child DOM relationship.

Fix: pass asChild to each of the three ContextMenuTrigger instances so
Radix's Slot mechanism merges the trigger props onto the row's own div.
This matches every other ContextMenuTrigger usage in the codebase
(tabs/tab-item, automations-page, settings/skills-settings,
settings/mcp-settings, conversations/sidebar-conversation-list, etc.).