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

Implementation Summary

This merge request implements the complete ship damage tracking and game completion functionality for US-03.

Requirements Implemented

✅ 1) Track hits per ship and determine when all squares of a ship are hit

• Ship class tracks hits per position with boolean array
• isSunk() method checks if all positions are hit
• getHitCount() method provides current damage status

✅ 2) Upon completion, announce the ship as 'sunk'

• Ship sinking detection in Board.allShipsSunk()
• Game state management in Game.executeShot()
• Integration with game flow for announcements

✅ 3) When all ships of a player are sunk, declare victory for the opponent and disable further input

• Game.getWinner() method identifies winner
• Game.executeShot() throws IllegalStateException when game finished
• Player.hasLost() method checks if player has lost

✅ 4) Provide New Game to start a fresh match

• GameService.createNewGame() resets all state
• Complete board and ship reset functionality

Acceptance Criteria Validated

✅ AC1: Given the last undamaged square of a ship is hit, when the result is processed, then that ship is announced 'sunk'

• Test: acceptanceCriterion1_lastUndamagedSquareHit_shipAnnouncedSunk()
• Validates ship sinking detection and announcement

✅ AC2: 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

• Test: acceptanceCriterion2_finalEnemyShipSunk_matchEndsWithWinnerAndNoFurtherShots()
• Validates game completion and input blocking

✅ AC3: Given a finished match, when New Game is chosen, then both boards reset to covered, unplaced state

• Test: acceptanceCriterion3_finishedMatch_newGameResetsBoards()
• Validates complete game state reset

Technical Implementation

Core Classes:

• Ship: Damage tracking with hits[] array and isSunk() method
• Board: Ship management with allShipsSunk() detection
• Game: Game state management with FINISHED state and winner determination
• Player: Loss detection with hasLost() method

Test Coverage:

• Comprehensive acceptance criteria tests in AcceptanceCriteriaTest_Issue3.java
• Additional validation tests for edge cases
• Integration tests for complete game flow

Files Modified/Created

Model Layer:

• Ship.java - Enhanced with damage tracking
• Board.java - Added ship sinking detection
• Game.java - Added game completion logic
• Player.java - Added loss detection

Service Layer:

• GameService.java - Game flow management

Test Layer:

• AcceptanceCriteriaTest_Issue3.java - Complete acceptance criteria validation

Closes #3