Fix: Pass WOPISrc directly to form submission, don't build URL with query params

- Remove URL building with query parameters that was causing GET requests
- Pass WOPISrc directly to _buildCollaboraIframe function
- JavaScript now creates form with POST method and WOPISrc in body
- This ensures Collabora receives POST not GET request

b0esche_cloud/lib/pages/document_viewer.dart

@@ -403,17 +403,8 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
 
         final wopiSession = snapshot.data!;
 
-        // Build Collabora Online viewer URL with WOPISrc
-        // 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);
+        // Don't build URL with query parameters - pass WOPISrc separately to JavaScript
+        return _buildWebView(wopiSession.wopisrc);
       },
     );
   }
@@ -457,16 +448,12 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
     }
   }
 
-  Widget _buildCollaboraIframe(String collaboraUrl) {
+  Widget _buildCollaboraIframe(String wopisrc) {
     // For Collabora Online, we need to POST the WOPISrc, not GET it
     // Use JavaScript to create and submit the form properly
     final String viewType = 'collabora-form-${DateTime.now().millisecondsSinceEpoch}';
 
     ui.platformViewRegistry.registerViewFactory(viewType, (int viewId) {
-      // Extract the WOPISrc from the URL
-      final uri = Uri.parse(collaboraUrl);
-      final wopisrc = uri.queryParameters['WOPISrc'] ?? '';
-
       // Create a container for the form and iframe
       final container = html.DivElement()
         ..style.width = '100%'
@@ -531,9 +518,9 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
     return HtmlElementView(viewType: viewType);
   }
 
-  Widget _buildWebView(String url) {
+  Widget _buildWebView(String wopisrc) {
     // Embed Collabora Online in an iframe for web platform
-    return _buildCollaboraIframe(url);
+    return _buildCollaboraIframe(wopisrc);
   }
 
   @override