Add GET_CONTENT picker support, fix account/login bugs, restyle selection UI

- Let Noo be picked as a source (Files + Photos) by other apps' native
  file/photo pickers via Android's GET_CONTENT intent, mirroring the
  existing "Share to Noo" plumbing: MainActivity.kt/PickIntentService/
  PickRequest, ServerProvider.pickRequest/confirmPick/cancelPick, and
  pick-mode tap handling in FilesView/PhotosView. While picking, the
  bottom nav and MoreTabsButton are restricted to Files/Photos only.
- Fix two account bugs: testConnection() failures no longer delete a
  still-valid stored app password (only an actual 401 does), and
  switchAccount() now retries a nominally-active-but-logged-out account
  instead of no-op'ing - both were silently locking users out of "Continue
  as" with no way back in except removing and re-adding the account
  (now exposed via login_view.dart's inline remove button).
- Fix the login WebView: clear cookies before every load so "Add Account"
  can't silently reuse an existing session, and push it as a
  non-animated route to avoid a known WebView-as-PlatformView black-screen-
  on-pop issue under Impeller.
- Redesign the Files/Photos selection toolbar to take over the top app bar
  entirely (SyncedHeaderScaffold.selectionBar) instead of sitting as a
  second bar under the controls row, with a horizontally-scrollable,
  uniformly-colored actions row and the same one-shot scroll-hint nudge
  the controls row uses.
- Redesign ShareUploadView to share the same SyncedHeaderScaffold chrome
  as every tab, with the uploading-file summary (marqueed via the new
  shared MarqueeTitle widget) and upload button grouped into one
  rounded/elevated bottom sheet.
- Restyle ShareSheet to open on the same DetailsHeader every other
  per-item sheet uses, and fix a couple of small design-language drifts
  (hardcoded text style, a non-rounded icon).
- Settings' account card: icon buttons with tooltips instead of text
  buttons for refresh/logout/remove, divider removed.

lib/widgets/share_sheet.dart

@@ -5,6 +5,7 @@ import '../models/nextcloud_item.dart';
 import '../models/nextcloud_share.dart';
 import '../models/nextcloud_sharee.dart';
 import '../providers/server_provider.dart';
+import 'details/details_sheet.dart' show DetailsHeader;
 import 'gradual_bottom_sheet.dart';
 
 IconData _shareTypeIcon(ShareType type) {
@@ -217,12 +218,15 @@ class _ShareSheetState extends State<ShareSheet> {
   }
 
   Widget _sectionHeader(String label) {
-    final colorScheme = Theme.of(context).colorScheme;
+    final theme = Theme.of(context);
+    final colorScheme = theme.colorScheme;
     return Row(
       children: [
         Text(
           label,
-          style: const TextStyle(fontWeight: FontWeight.w700, fontSize: 15),
+          style: theme.textTheme.titleSmall?.copyWith(
+            fontWeight: FontWeight.w700,
+          ),
         ),
         const SizedBox(width: 6),
         Icon(
@@ -301,17 +305,16 @@ class _ShareSheetState extends State<ShareSheet> {
 
     return ListView(
       controller: widget.scrollController,
-      padding: const EdgeInsets.fromLTRB(20, 12, 20, 24),
+      padding: const EdgeInsets.fromLTRB(20, 0, 20, 24),
       children: [
-        Text(
-          widget.item.name,
-          maxLines: 1,
-          overflow: TextOverflow.ellipsis,
-          style: theme.textTheme.titleMedium?.copyWith(
-            fontWeight: FontWeight.w700,
-          ),
+        // Same icon/name/meta header as DetailsSheet, so this and its
+        // sibling per-item bottom sheet open on identical chrome - just a
+        // bare title `Text` here read as under-designed by comparison.
+        DetailsHeader(
+          item: widget.item,
+          padding: const EdgeInsets.only(top: 12, bottom: 8),
         ),
-        const SizedBox(height: 16),
+        const SizedBox(height: 8),
         _sectionHeader('Internal shares'),
         const SizedBox(height: 8),
         TextField(
@@ -380,7 +383,7 @@ class _ShareSheetState extends State<ShareSheet> {
           keyboardType: TextInputType.emailAddress,
           decoration: InputDecoration(
             hintText: 'Type an email',
-            prefixIcon: const Icon(Icons.email_outlined),
+            prefixIcon: const Icon(Icons.email_rounded),
             border: OutlineInputBorder(borderRadius: BorderRadius.circular(16)),
             filled: true,
             fillColor: colorScheme.surfaceContainerLow,