fix: rename Open to View Details and hide empty Details section (refs #43)

- Rename "Open" button to "View Details" on desktop and mobile document lists
- Add hasDisplayableMetadata helper to check if document has metadata to display
- Conditionally render Details section only when metadata exists
- Prevents showing empty "Details" header for documents without metadata

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/features/documents/pages/DocumentsPage.tsx

@@ -158,7 +158,7 @@ export const DocumentsPage: React.FC = () => {
                     </div>
                   )}
                   <div className="flex gap-2 pt-2">
-                    <Button onClick={() => navigate(`/garage/documents/${doc.id}`)}>Open</Button>
+                    <Button onClick={() => navigate(`/garage/documents/${doc.id}`)}>View Details</Button>
                     <Button variant="danger" onClick={() => removeDoc.mutate(doc.id)}>Delete</Button>
                   </div>
                 </div>