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>

pubspec.lock

@@ -161,6 +161,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.0"
+  fading_edge_scrollview:
+    dependency: transitive
+    description:
+      name: fading_edge_scrollview
+      sha256: "1f84fe3ea8e251d00d5735e27502a6a250e4aa3d3b330d3fdcb475af741464ef"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.1.1"
   fake_async:
     dependency: transitive
     description:
@@ -456,6 +464,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.3.0"
+  marquee:
+    dependency: "direct main"
+    description:
+      name: marquee
+      sha256: a87e7e80c5d21434f90ad92add9f820cf68be374b226404fe881d2bba7be0862
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.3.0"
   matcher:
     dependency: transitive
     description:
@@ -704,6 +720,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.2.1"
+  receive_sharing_intent:
+    dependency: "direct main"
+    description:
+      name: receive_sharing_intent
+      sha256: ec76056e4d258ad708e76d85591d933678625318e411564dcb9059048ca3a593
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.8.1"
   record_use:
     dependency: transitive
     description: