feat: Add "Create subtask" option to task card context menu (#192)

Add a new "Create subtask" menu item to the task card context menu that
creates a new task with the current task as the project reference. This
provides the same functionality as the "New" button in the project
subtasks widget but is accessible from any task card.

Author: callumalpass

src/ui/TaskCard.ts

@@ -728,6 +728,22 @@ export async function showTaskContextMenu(event: MouseEvent, taskPath: string, p
 
         menu.addSeparator();
 
+        // Create subtask
+        menu.addItem((item) => {
+            item.setTitle('Create subtask');
+            item.setIcon('plus');
+            item.onClick(() => {
+                // Create a subtask with the current task as the project reference
+                const taskFile = plugin.app.vault.getAbstractFileByPath(task.path);
+                if (taskFile instanceof TFile) {
+                    const projectReference = `[[${taskFile.basename}]]`;
+                    plugin.openTaskCreationModal({
+                        projects: [projectReference]
+                    });
+                }
+            });
+        });
+        
         // Delete Task
         menu.addItem((item) => {
             item.setTitle('Delete task');