Add share-to-upload, per-folder sort, and media viewer polish

- Accept Android's "Share to..." intent (ACTION_SEND/SEND_MULTIPLE) to
  upload a shared file, with a new destination-folder picker screen
- Unlink Files/Photos sort settings and make Files remember sort
  per folder (like per-folder view settings), instead of one shared
  global sort field for both tabs
- Media viewer: show the file name (marquee-scrolling if too long) in
  the top bar next to a resized back button, slide the top bar out of
  view instead of fading it, and unify icon color/contrast across the
  top bar, bottom action bar, and video transport controls
- Add a scrollbar thumb to every scrollable list in the app (all tab
  views via SyncedHeaderScaffold, search results, settings, the new
  upload folder picker, share sheet, and the Details sheet's tabs)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/widgets/details/details_info_tab.dart

@@ -26,39 +26,42 @@ class DetailsInfoTab extends StatelessWidget {
       ('Favorite', item.isFavorite ? 'Yes' : 'No'),
     ];
 
-    return ListView.separated(
+    return Scrollbar(
       controller: scrollController,
-      padding: const EdgeInsets.fromLTRB(20, 12, 20, 24),
-      itemCount: rows.length,
-      separatorBuilder: (context, index) => const Divider(height: 1),
-      itemBuilder: (context, index) {
-        final (label, value) = rows[index];
-        return Padding(
-          padding: const EdgeInsets.symmetric(vertical: 12),
-          child: Row(
-            crossAxisAlignment: CrossAxisAlignment.start,
-            children: [
-              SizedBox(
-                width: 96,
-                child: Text(
-                  label,
-                  style: theme.textTheme.bodyMedium?.copyWith(
-                    color: colorScheme.onSurfaceVariant,
+      child: ListView.separated(
+        controller: scrollController,
+        padding: const EdgeInsets.fromLTRB(20, 12, 20, 24),
+        itemCount: rows.length,
+        separatorBuilder: (context, index) => const Divider(height: 1),
+        itemBuilder: (context, index) {
+          final (label, value) = rows[index];
+          return Padding(
+            padding: const EdgeInsets.symmetric(vertical: 12),
+            child: Row(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                SizedBox(
+                  width: 96,
+                  child: Text(
+                    label,
+                    style: theme.textTheme.bodyMedium?.copyWith(
+                      color: colorScheme.onSurfaceVariant,
+                    ),
                   ),
                 ),
-              ),
-              Expanded(
-                child: Text(
-                  value,
-                  style: theme.textTheme.bodyMedium?.copyWith(
-                    fontWeight: FontWeight.w500,
+                Expanded(
+                  child: Text(
+                    value,
+                    style: theme.textTheme.bodyMedium?.copyWith(
+                      fontWeight: FontWeight.w500,
+                    ),
                   ),
                 ),
-              ),
-            ],
-          ),
-        );
-      },
+              ],
+            ),
+          );
+        },
+      ),
     );
   }
 }