[US-02] Take turns firing with hit/miss feedback

Implementation Summary

This merge request implements the turn-based firing mechanics for the Battleship game as specified in Issue #2.

Requirements Implemented

1. Enforce alternating turns - Game logic ensures players take turns
2. Target coordinate selection - Players can select coordinates on opponent's grid
3. Hit/miss feedback - Immediate feedback with ShotResult class
4. Prevent duplicate firing - Coordinate tracking prevents repeated shots

Key Features Added

• ShotResult class to encapsulate shot outcomes (HIT, MISS, ALREADY_TARGETED)
• Turn management in Game class
• Coordinate validation and tracking
• Comprehensive test coverage for all acceptance criteria

Acceptance Criteria Verified

• ✅ Given A1 has not been targeted, when the player fires at A1, then the result is shown (hit/miss) and A1 becomes marked as used
• ✅ Given A1 is already targeted, when the player attempts A1 again, then the system blocks the action and preserves turn order rules
• ✅ Given a turn completes, when control passes, then only the next player can act

Pipeline Status

• Previous successful pipeline: #6603 ✅
• Current pipeline: #6616 (running)

Closes #2