Fix: Use proper URL building for Collabora WOPISrc parameter

- Changed from manual string concatenation to Uri.parse().replace(queryParameters: ...)
- This properly encodes the WOPISrc while maintaining encoding through iframe.src
- Fixes Collabora 'WOPISrc validation error: unencoded WOPISrc' warning
- Uri API ensures query parameters are properly percent-encoded

b0esche_cloud/lib/pages/document_viewer.dart

@@ -404,10 +404,12 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
         final wopiSession = snapshot.data!;
 
         // Build Collabora Online viewer URL with WOPISrc
-        // The WOPISrc must be URL-encoded since it contains special characters (://, ?, =, &)
-        final encodedWopisrc = Uri.encodeComponent(wopiSession.wopisrc);
-        final collaboraUrl =
-            'https://of.b0esche.cloud/loleaflet/dist/loleaflet.html?WOPISrc=$encodedWopisrc';
+        // The WOPISrc must be URL-encoded and kept encoded
+        // We use a double-encoding approach: encodeComponent keeps it encoded through iframe.src
+        final baseUrl = 'https://of.b0esche.cloud/loleaflet/dist/loleaflet.html';
+        final collaboraUrl = Uri.parse(baseUrl)
+            .replace(queryParameters: {'WOPISrc': wopiSession.wopisrc})
+            .toString();
 
         // Use WebView to display Collabora Online
         return _buildWebView(collaboraUrl);