feat: Integrate JS Gantt Chart library and update styles

- Added JS Gantt Chart library files including CSS and JS.
- Updated existing Gantt chart styles for better visual representation.
- Translated month and day names to Polish in the Gantt chart settings.
- Implemented Gantt chart initialization in the main view with sample data.
- Added a toggle switch for displaying tasks in the calendar.
- Enhanced task edit form with a new checkbox for calendar visibility.
- Improved the layout of the logged-in user template to include Gantt chart styles and scripts.

libraries/JS-Gantt-Chart-master/.gitattributes

@@ -0,0 +1,2 @@
+# Auto detect text files and perform LF normalization
+* text=auto