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>

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.23.0
+
+- Run tab file inputs accept a host-injected native file picker
+  (`FlowEditorPage.onPickFile`, new `PickedFileData` /
+  `PickFileCallback` contract). The manual path-entry dialog remains
+  only as the no-host fallback — typing an absolute path by hand is
+  a last resort, not an input method.
+
 All notable changes to `chain_studio_flow_editor` recorded here.
 Studio bumps its `pubspec.yaml` git ref to a specific release
 of this package on every editor change.