feat: add pinned tag functionality and UI enhancements

- Introduced `isPinned` property to the `Tag` model for marking main objectives.
- Updated `TagForm` to include a checkbox for setting tags as pinned, enhancing user interaction.
- Enhanced `KanbanBoardContainer` to display pinned tasks in a dedicated `ObjectivesBoard`, improving task visibility.
- Modified `KanbanFilters` to support filtering by pinned tags, streamlining task management.
- Adjusted `TasksContext` to separate pinned tasks from regular tasks for better organization.

components/kanban/KanbanFilters.tsx

@@ -13,6 +13,7 @@ export interface KanbanFilters {
   showCompleted?: boolean;
   compactView?: boolean;
   swimlanesByTags?: boolean;
+  pinnedTag?: string; // Tag pour les objectifs principaux
 }
 
 interface KanbanFiltersProps {
@@ -66,6 +67,13 @@ export function KanbanFilters({ filters, onFiltersChange }: KanbanFiltersProps)
     });
   };
 
+  const handlePinnedTagChange = (tagName: string | undefined) => {
+    onFiltersChange({ 
+      ...filters, 
+      pinnedTag: tagName
+    });
+  };
+
   const handleClearFilters = () => {
     onFiltersChange({});
   };