feat: show shared items in main Library view

[scottgrayson]

Summary

• Adds orWhereHas('permissions') to the root-level query in ListLibraryItems so items explicitly shared with a user appear in the main Library view (not just "Shared with Me")
• Adds a "Shared with you" description label on items shared with the current user
• Only surfaces root-level shared items (whereNull('parent_id') still applies); items inside personal folders remain in "Shared with Me"

Test plan

• Admin creates a root-level private folder, shares with User B → User B sees it in Library root
• Admin creates a folder inside their personal folder, shares with User B → User B sees it in "Shared with Me" only (NOT at root)
• Public folder with explicit share → no duplicate display
• Unsharing removes item from user's Library view
• "Shared with Me" page still works (no regression)
• Files and links (not just folders) work in all scenarios

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