fix: add credentials to frontend fetch calls for auth middleware

[cfsmp3]

Summary

• Frontend fetch calls to task API endpoints were missing credentials: 'include'
• The auth middleware added in PR security: inject session credentials into API requests #408 requires session cookies on all protected endpoints
• Without credentials, requests return 401 "Authentication required", causing tasks not to display in the UI

Files Changed

• frontend/src/components/HomeComponents/Tasks/hooks.ts - Added credentials: 'include' to fetchTaskwarriorTasks, addTaskToBackend, editTaskOnBackend, modifyTaskOnBackend
• frontend/src/components/HomeComponents/Tasks/tasks-utils.ts - Added credentials: 'include' to markTaskAsCompleted, bulkMarkTasksAsCompleted, bulkMarkTasksAsDeleted, markTaskAsDeleted

Test plan

• Log in to the frontend
• Verify tasks are displayed correctly
• Add a new task and verify it appears
• Complete/delete a task and verify it updates

🤖 Generated with Claude Code

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