fix: preserve new task drafts and restore task list rendering

[rachit23tech]

Related Issue

Closes #580

Summary

Fixes the new task creation flow so opening the deadline picker no longer closes the form or discards unsaved input. It also restores task card rendering in the task list, which previously showed the pending count button without displaying the actual task items.

Changes Made

• Prevented the new task modal from closing on backdrop clicks.
• Added explicit modal close handling through Cancel, close button, and Escape.
• Added unsaved-draft confirmation before discarding new task form input.
• Kept the native datetime-local input and widened/repositioned the modal on desktop so the picker has room to open beside the form.
• Updated post-save calendar behavior to focus the saved task’s due date in calendar view.
• Fixed task list markup assembly so pending tasks render correctly again.
• Added helper modules for new-task modal state handling and safe markup joining.
• Added regression tests for modal draft-state behavior, post-save calendar focus, and task markup joining.

Testing

Tested locally with:

• node --test .\tests\exportIcs.test.js .\tests\newTaskModal.test.mjs .\tests\taskMarkup.test.mjs
  Result:
• 14 tests passed
• 0 tests failed

Screenshots

Checklist

• Code follows project style
• Tested locally
• No unrelated changes included
• Documentation updated (if applicable)

[rachit23tech]

Hi @Charushi06

I have made the necessary fixes and sent in PR.
Kindly review it and merge it in.

Update me if any changes are needed.