Feature: Show subject in assignment list

[xenonnn4w]

Summary

Add the assignment’s subject to the CLI list output (was briefly added, then reverted to let others contribute).

Current Behavior

python main.py list shows only title and deadline.

Expected Behavior

python main.py list should show subject when available, e.g.:

• Math HW 1 [Subject: Algebra] (Due: 2025-01-20)
• Essay Draft [Subject: English] (Due: 2025-01-25)
  If no subject is set, show a fallback like No subject.

Proposed Changes

• Update main.py list command output to include subject.
• Keep behavior backward-compatible; no extra flags required.

Files to Touch

• main.py (list display)

Acceptance Criteria

• Subject shown for assignments that have it.
• Graceful fallback when subject is missing.
• No change to other commands.
• Basic test or manual run example attached.

[SourajyotiKarmakar25]

Hi, I wish to contribute. I will be fixing the issue by adding subject in the display.
When subject is missing, I would prefer the display to show me only Title and Date. I can do that by adding a separate conditional branch. Mentioning "No Subject" will just clutter things unnecessarily.