feat: Implement US-01 - Ship placement functionality

Implementation of US-01: Setting ships somewhere on the board

Requirements Implemented:

• ✅ 10x10 game board for each player
• ✅ Standard ship types: Carrier (5), Battleship (4), Cruiser (3), Submarine (3), Destroyer (2)
• ✅ Ship placement validation (straight placement only, no diagonals)
• ✅ Overlap prevention between ships
• ✅ Board boundary validation
• ✅ Hidden ship positions from opponent

Core Components:

• Board: Manages 10x10 grid with ship placement and validation
• Ship: Represents individual ships with type, position, and orientation
• Player: Manages player's board and ship placement
• Coordinate: Handles grid coordinates with validation
• Cell: Represents individual board cells with ship and hit status

Validation & Error Handling:

• Ships placed outside board boundaries are rejected
• Overlapping ship placements are rejected
• All ships must be placed before game can proceed
• Ship positions remain hidden from opponent

Acceptance Criteria Verified:

• ✅ Ship outside board → Placement fails with error
• ✅ Overlapping ships → Second placement fails (no overwrite)
• ✅ All ships placed validly → Board ready for gameplay

Testing:

• Comprehensive unit tests for all validation scenarios
• Acceptance criteria tests explicitly implemented
• Test coverage for edge cases and boundary conditions

Closes #1