Add deleteByValue and menu option to LinkedList demo

[Nullkernel]

Motivation

• Provide a convenient way to remove the first node matching a value from the singly linked list without using a position index.
• Make the CLI demo cover deletion-by-value so users can exercise the new operation interactively.

Description

• Added deleteByValue(int key) to SinglyLinkedList which handles an empty list, removes the head when it matches, traverses with prev/curr to unlink the first matching node, and prints a clear message when no node matches.
• Updated the interactive menu in LinkedList.main to include a Delete by Value option and adjusted subsequent menu numbering and the loop exit condition accordingly.
• Kept existing deletion-by-position and other list operations unchanged except for menu wiring.

Testing

• Ran javac Data-Structures/Linked-Lists/LinkedList.java and compilation completed successfully.

---

Codex Task