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/views/account_view.dart

@@ -102,8 +102,6 @@ class AccountView extends StatelessWidget {
                     ],
                   ),
                   const SizedBox(height: 16),
-                  const Divider(height: 1),
-                  const SizedBox(height: 16),
                   Row(
                     mainAxisAlignment: MainAxisAlignment.spaceBetween,
                     children: [
@@ -188,62 +186,35 @@ class AccountView extends StatelessWidget {
                   const Divider(height: 1),
                   const SizedBox(height: 16),
                   Row(
+                    mainAxisAlignment: MainAxisAlignment.end,
                     children: [
-                      Expanded(
-                        child: OutlinedButton(
-                          onPressed: () async {
-                            await provider.refreshData();
-                            if (context.mounted) {
-                              ScaffoldMessenger.of(context).showSnackBar(
-                                const SnackBar(
-                                  content: Text('Refreshed WebDAV data'),
-                                  behavior: SnackBarBehavior.floating,
-                                ),
-                              );
-                            }
-                          },
-                          style: OutlinedButton.styleFrom(
-                            padding: const EdgeInsets.symmetric(vertical: 12),
-                          ),
-                          child: const Text(
-                            'Refresh Cache',
-                            textAlign: TextAlign.center,
-                            style: TextStyle(fontSize: 13),
-                          ),
-                        ),
+                      IconButton(
+                        icon: const Icon(Icons.refresh_rounded),
+                        tooltip: 'Refresh cached data',
+                        onPressed: () async {
+                          await provider.refreshData();
+                          if (context.mounted) {
+                            ScaffoldMessenger.of(context).showSnackBar(
+                              const SnackBar(
+                                content: Text('Refreshed WebDAV data'),
+                                behavior: SnackBarBehavior.floating,
+                              ),
+                            );
+                          }
+                        },
                       ),
-                      const SizedBox(width: 8),
-                      Expanded(
-                        child: FilledButton(
-                          onPressed: () => _handleLogout(context, provider),
-                          style: FilledButton.styleFrom(
-                            backgroundColor: colorScheme.errorContainer,
-                            foregroundColor: colorScheme.onErrorContainer,
-                            padding: const EdgeInsets.symmetric(vertical: 12),
-                          ),
-                          child: const Text(
-                            'Logout',
-                            textAlign: TextAlign.center,
-                            style: TextStyle(fontSize: 13),
-                          ),
-                        ),
+                      IconButton(
+                        icon: const Icon(Icons.logout_rounded),
+                        tooltip: 'Logout',
+                        color: Colors.orange.shade700,
+                        onPressed: () => _handleLogout(context, provider),
                       ),
-                      const SizedBox(width: 8),
-                      Expanded(
-                        child: FilledButton(
-                          onPressed: () =>
-                              _confirmRemoveActive(context, provider),
-                          style: FilledButton.styleFrom(
-                            backgroundColor: colorScheme.error,
-                            foregroundColor: colorScheme.onError,
-                            padding: const EdgeInsets.symmetric(vertical: 12),
-                          ),
-                          child: const Text(
-                            'Remove',
-                            textAlign: TextAlign.center,
-                            style: TextStyle(fontSize: 13),
-                          ),
-                        ),
+                      IconButton(
+                        icon: const Icon(Icons.delete_outline_rounded),
+                        tooltip: 'Remove account',
+                        color: colorScheme.error,
+                        onPressed: () =>
+                            _confirmRemoveActive(context, provider),
                       ),
                     ],
                   ),