Fix: modal scroll behavior

[KrithikaVellingiri]

📌 Description

This PR improves the TaskFormModal UX and fixes multiple modal positioning and scroll behavior issues in the Routine Builder flow.

Previously, the modal could appear inconsistently when opened from deeper sections of the page, especially from the Saved Routines EmptyState. These changes make the modal behavior smoother, more stable, and more consistent across the application.

🔗 Related Issue

Closes #320

🛠 Changes Made

• Added portal-based modal rendering using createPortal
• Improved modal overlay and backdrop behavior
• Added scroll-then-open workflow for EmptyState actions
• Added fixed-body scroll locking and scroll restoration
• Improved modal positioning and responsiveness
• Added Escape key and backdrop close handling
• Refactored modal open/close logic in RoutineBuilder

📸 Screenshots (if applicable)

before.vs.after.mp4

✅ Checklist

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

[Sushmitha224ai]

i would like to fix scroll behaviour under gssoc please assign it to me