[US-04] Single-player mode vs. computer opponent

Implementation Summary

This merge request implements single-player mode with computer opponent functionality for the Battleship game.

Features Implemented

• Computer Player AI: Computer opponent with Easy and Standard difficulty levels
• Ship Placement: Computer automatically places legal fleet (no overlaps/out-of-bounds)
• Turn Management: Computer selects valid untargeted coordinates and avoids repeats
• Difficulty Levels:
  • Easy: Random shots
  • Standard: Hunting strategy - after a hit, preferentially targets adjacent cells

Technical Implementation

• Created ComputerPlayer class extending Player with AI logic
• Created GameService for single-player game flow management
• Created Game and GameState classes for game state management
• Updated existing classes (Ship, Cell) for game logic integration

Acceptance Criteria Coverage

• Criterion 1: Computer fleet exists and is legal but hidden
• Criterion 2: Computer shots are at previously untargeted coordinates
• Criterion 3: Standard difficulty hunting strategy targets adjacent cells after hits

Current Status

Pipeline Status: FAILED (#8751) Compilation: SUCCESS Tests: 79 tests run, 11 failures, 15 errors

Critical Issues Identified

1. ComputerPlayer.placeShipsAutomatically() - Fails to place ships successfully
2. Game.startGame() - Doesn't transition game state from SETUP to IN_PROGRESS
3. Turn Management - "Not computer player's turn" errors in test execution

Next Steps Required

• Coding Agent needs to fix the identified implementation issues
• ComputerPlayer ship placement must be corrected
• Game state transitions must be fixed
• Turn management logic must be resolved

Closes #4