[US-03] Track ship damage, announce sunk, and end the game

Description

This merge request implements the third user story for the Battleship game: tracking ship damage, announcing when ships are sunk, and ending the game when a fleet is destroyed.

Requirements Implemented

1. Track hits per ship - Implemented damage tracking for each ship
2. Announce ship as 'sunk' - Added logic to detect when all squares of a ship are hit
3. End game when fleet destroyed - Added victory detection and game end logic
4. Provide New Game functionality - Implemented game reset capability

Acceptance Criteria Verified

• ✅ Given the last undamaged square of a ship is hit, when the result is processed, then that ship is announced 'sunk'.
• ✅ Given the final enemy ship is sunk, when the board updates, then the match ends, the winner is indicated, and no further shots are allowed.
• ✅ Given a finished match, when New Game is chosen, then both boards reset to covered, unplaced state.

Technical Implementation

• Added Ship entity with damage tracking and sunk status
• Enhanced Game class with victory detection logic
• Implemented game state management for end-game scenarios
• Added comprehensive test coverage for all acceptance criteria

Testing

All acceptance criteria are covered by unit tests in Issue3AcceptanceCriteriaTest.java:

• Test for ship sinking detection
• Test for game end condition
• Test for new game functionality

Closes #3