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/gantt.css

@@ -0,0 +1,106 @@
+.gfb-gantt-wrapper {
+  --entry-color: #033b6a;
+  --border-color: rgba(0, 0, 0, 0.1);
+  --background-color: #f9f9f9;
+  --hovered-background: #f0f0f0;
+}
+
+.gfb-gantt-wrapper {
+  position: relative;
+  min-width: 550px;
+}
+
+.gfb-gantt-headers {
+  display: grid;
+  background-color: var(--background-color);
+  border: 1px solid var(--border-color);
+  min-height: 40px;
+}
+
+.gfb-gantt-headers>div:not(:last-child) {
+  border-right: 1px solid var(--border-color);
+}
+
+.gfb-gantt-header {
+  display: flex;
+  padding: 5px 0px 5px 5px;
+}
+
+.gfb-gantt-sidebar-header {
+  text-align: center;
+  padding: 10px 5px 10px 5px;
+  background-color: var(--background-color);
+  border-right: 1px solid var(--border-color);
+}
+
+.gfb-gantt-content {
+  position: relative;
+}
+
+.gfb-gantt-row {
+  display: grid;
+  min-height: 25px;
+  border: 1px solid var(--border-color);
+  border-top: 0;
+  border-right: 1px solid transparent;
+
+}
+
+.gfb-gantt-sub-row-wrapper {
+  max-height: 15px;
+  display: flex;
+  width: 100%;
+  height: 100%;
+}
+
+.gfb-gantt-row-entry {
+  border-radius: 10px;
+  cursor: pointer;
+  background-color: var(--entry-color);
+}
+
+.gfb-gantt-row-entry:hover {
+  box-shadow: var(--entry-color) 0px 0px 2px .1px;
+}
+
+.gfb-gantt-lines-container {
+  display: grid;
+  position: absolute;
+  top: 0;
+  left: 0;
+  height: 100%;
+  width: 100%;
+  border: 1px solid var(--border-color);
+  z-index: 0;
+}
+
+.gfb-gantt-lines-container>div:not(:last-child):not(.gfb-gantt-sidebar-template) {
+  border-right: 1px solid var(--border-color);
+}
+
+.gfb-gantt-row-entry-tooltip {
+  position: absolute;
+  display: none;
+  max-width: 400px;
+  background-color: #ffffff;
+  box-shadow: 0 0 5px #aaa;
+  padding: 10px;
+  z-index: 20;
+}
+
+.gfb-gantt-grouping-header {
+  background-color: var(--background-color);
+  padding: 5px 0;
+  border: 1px solid var(--border-color);
+  border-top: 0 transparent;
+  cursor: pointer;
+  user-select: none;
+}
+
+.gfb-gantt-grouping-header:hover {
+  background-color: var(--hovered-background);
+}
+
+.gfb-gantt {
+  overflow: auto;
+}