feat: improve task creation to support multiple URLs.

[arabcoders]

• Added support in the API (POST /api/tasks) for submitting an array of task objects, with logic to backfill missing fields from the first task, infer names from URL metadata, and offset CRON timers by 5-minute increments for each subsequent task to avoid simultaneous execution.
• Enhanced the TaskForm.vue component to support multi-line URL input (shift+enter or paste), dynamically switch between input and textarea, and display a summary/info message when multiple URLs are detected.
• Implemented logic to split the input into multiple tasks, emit all tasks on submit, and show the URL count and multi-URL instructions in the UI.
• Refactored tasks_add route to accept a list of tasks, inherit settings, apply timer offsets, infer names, and return all created tasks in the response.
• Expanded API documentation to clearly explain new multi-task creation, field inheritance, name/timer logic, and response format.