docs(progressbar): added docs

docs/user/widgets/bec_progressbar/bec_progressbar.md

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+(user.widgets.bec_progressbar)=
+# BEC Progressbar
+
+```{tab} Overview
+
+The BEC Progressbar widget is a general purpose progress bar that follows the BEC theme and style. It can be embedded in any application to display the progress of a task or operation. 
+
+## Key Features:
+- **Modern Design**: The BEC Progressbar widget is designed with a modern and sleek appearance, following the BEC theme.
+- **Customizable**: Users can customize the appearance and behavior of the progress bar to suit their application.
+- **Responsive**: The progress bar updates in real-time to reflect the progress of the task or operation.
+
+## Screenshot
+![BEC Progressbar](./bec_progressbar_running.png)
+![BEC Progressbar](./bec_progressbar_completed.png)
+
+```
+
+````{tab} Examples
+
+The `BECProgressBar` widget can be integrated within a [`BECDockArea`](user.widgets.bec_dock_area) or used as an individual component in your application through `BECDesigner`. Below are examples demonstrating how to create and use the `BECProgressBar` widget.
+
+## Example 1 - Adding BEC Status Box to BECDockArea
+
+In this example, we demonstrate how to add a `BECProgressBar` widget to a `BECDockArea`, allowing users to manually set and update the progress states.
+
+```python
+# Add a new dock with a BECStatusBox widget
+pb = gui.add_dock().add_widget("BECProgressBar")
+pb.set_value(50)
+```
+
+````
+
+````{tab} API
+```{eval-rst} 
+.. include:: /api_reference/_autosummary/bec_widgets.cli.client.BECProgressbar.rst
+```
+````