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.

.vscode/ftp-kr.sync.cache.json

@@ -56,20 +56,20 @@
       "layout": {
         "style.css": {
           "type": "-",
-          "size": 21838,
-          "lmtime": 1740644284491,
+          "size": 22346,
+          "lmtime": 1743623979088,
           "modified": false
         },
         "style.css.map": {
           "type": "-",
-          "size": 37961,
-          "lmtime": 1740644284491,
+          "size": 39015,
+          "lmtime": 1743623979088,
           "modified": false
         },
         "style.scss": {
           "type": "-",
-          "size": 26476,
-          "lmtime": 1740644284325,
+          "size": 27154,
+          "lmtime": 1743623978938,
           "modified": false
         }
       },
@@ -97,8 +97,8 @@
           },
           "main_view.php": {
             "type": "-",
-            "size": 28190,
-            "lmtime": 1740517008484,
+            "size": 29103,
+            "lmtime": 1743623929427,
             "modified": false
           },
           "task_edit.php": {
@@ -109,8 +109,8 @@
           },
           "task_popup.php": {
             "type": "-",
-            "size": 6222,
-            "lmtime": 0,
+            "size": 6272,
+            "lmtime": 1743622901914,
             "modified": false
           },
           "task_single.php": {