Validate task IDs in bulkDeleteTasks

[Snnehamaurya]

📌 Description

Added validation for task IDs in the bulkDeleteTasks controller to ensure all IDs are valid MongoDB ObjectIds before performing delete operations.

🔗 Related Issue

Closes #1358

🛠 Changes Made

• Added validation for each task ID using mongoose.Types.ObjectId.isValid()
• Return 400 Bad Request when an invalid task ID is provided
• Prevent Mongoose cast errors from causing 500 Internal Server Error responses

📸 Screenshots (if applicable)

N/A (Backend-only change)

✅ Checklist

• Followed project structure
• No console errors related to the implemented change
• Linked the issue
• Code runs locally
• Properly tested changes

🚀 Notes for Reviewers

This change validates all task IDs received in the bulk delete request before calling Task.deleteMany() and Routine.updateMany(). If any invalid ID is found, the API returns a 400 response with the message: "Invalid task ID provided".