fix(external-editor): Move panel to Operations Hub, fix config key lookup

- Moved External Editor panel from AI Settings to External Tools tab in Operations Hub
- Fixed default_editor lookup to use nested [tools.default_editor] structure
- Added example entries for vscode, notepadpp, 10xEditor, rider, sublime
- Improved panel UI with section header and clearer formatting

src/external_editor.py

@@ -50,7 +50,7 @@ def get_default_launcher() -> ExternalEditorLauncher:
     from src import models
     config = models.load_config()
     editors_config = config.get("tools", {}).get("text_editors", {})
-    default_editor = config.get("tools", {}).get("default_editor")
+    default_editor = config.get("tools", {}).get("default_editor", {}).get("default_editor")
     ext_config = ExternalEditorConfig.from_dict({
         "editors": editors_config,
         "default_editor": default_editor,