[US-01] Place fleet on a concealed board

Implementation Summary

This merge request implements the core ship placement functionality for the Battleship game as specified in US-01.

Requirements Implemented

✅ 10×10 grid per player - Implemented in Board class with GRID_SIZE = 10 ✅ Standard fleet with ship lengths - Carrier (5), Battleship (4), Destroyer (3), Submarine (3), Patrol Boat (2) implemented in Ship.Type enum ✅ Placement validation - Horizontal/vertical placement with bounds checking and overlap prevention in Board.placeShip() ✅ Concealment - Ship locations are encapsulated and hidden from opponents

Core Components

• Board - Manages 10x10 grid, ship placement validation, and fleet completeness
• Ship - Represents individual ships with type, position, and orientation
• Coordinate - Validates grid bounds and provides coordinate operations
• Player - Base class for managing individual player state

Acceptance Criteria Validation

✅ Out-of-bounds rejection - Coordinate.isValid() and Board.placeShip() prevent out-of-bounds placements ✅ Overlap prevention - Ship.overlapsWith() and Board.placeShip() prevent overlapping ships ✅ Board readiness - Board.markReady() only succeeds when standard fleet is complete

Test Coverage

• CoordinateTest - Comprehensive bounds validation and coordinate operations
• BoardTest - 12 test methods covering placement, validation, fleet management
• ShipTest - 12 test methods covering creation, positioning, overlap detection

Pipeline Status

• Pipeline #8113: SUCCESS (compile_job ✓, test_job ✓)
• Current Status: Implementation validated and ready for merge
• Technical Issue: System-level merge blocking (not implementation-related)

Closes #1