feat(run): host-injected native file picker for flow file inputs

The Run tab asked the operator to type an absolute path into a text
field — with no file dialog anywhere. FlowEditorPage now accepts an
onPickFile callback (PickedFileData: name + bytes) that hosts wire
to their native picker; the path-entry dialog remains only as the
no-host fallback. 0.23.0.

Signed-off-by: flemming-it <sf@flemming.it>

lib/src/flow_editor_page.dart

@@ -101,6 +101,11 @@ class FlowEditorPage extends StatefulWidget {
   /// silent — no install button offered.
   final List<String> storeCapabilities;
 
+  /// Host-side native file picker for the Run tab's file inputs.
+  /// Studio passes a real file dialog; null keeps the manual
+  /// path-entry fallback.
+  final PickFileCallback? onPickFile;
+
   /// The host's active workspace/project slug (empty = "all
   /// projects", no active workspace). Used only to flag a
   /// mismatch when the open flow file declares a *different*
@@ -126,6 +131,7 @@ class FlowEditorPage extends StatefulWidget {
     this.storeCapabilities = const [],
     this.activeProject = '',
     this.onSwitchToFileProject,
+    this.onPickFile,
   });
 
   @override
@@ -658,6 +664,7 @@ outputs:
                 controller: _controller,
                 strings: _l,
                 driver: widget.runDriver,
+                onPickFile: widget.onPickFile,
               ),
             ],
           ),