[US-01] Place fleet on a concealed board

Implementation Summary

This merge request implements the foundation user story for the Battleship game - placing a fleet on a concealed board.

Requirements Implemented

✅ 10×10 grid per player - Board class with 10x10 grid implementation ✅ Standard fleet with ship lengths - ShipType enum with Carrier (5), Battleship (4), Destroyer (3), Submarine (3), Patrol Boat (2) ✅ Placement validation - Horizontal/vertical placement with rejection of diagonal, overlapping, or out-of-bounds placements ✅ Concealed ship locations - Each player's ship locations remain hidden from opponent

Core Entities Created

• Board: 10x10 grid with ship placement and shot tracking
• Ship: Individual ship with type, positions, and damage tracking
• Coordinate: Grid position management
• ShipType: Enum with standard fleet ship types and lengths
• Game: Main game controller (foundation for future stories)
• Player: Base player class
• GameState: Game state management

Acceptance Criteria Verified

✅ AC1: Given a ship partly outside the grid, when placement is attempted, then the system rejects it with an error and no placement occurs ✅ AC2: Given two ships sharing any square, when the second is placed, then placement is rejected and existing ships remain unchanged ✅ AC3: Given a valid layout, when all ships are placed, then the board is marked ready and remains hidden from the opponent

Technical Details

• Java 21 with Maven build system
• JUnit 5 tests with comprehensive coverage
• Layered architecture following planning documents
• All tests passing in successful pipeline #6565

Closes #1