[US-01] Place fleet on a concealed board

As a player I want to position my ships on a concealed grid So that I can start a fair game.

The system shall:

1. Provide a 10×10 grid per player.
2. Provide a standard fleet with ship lengths: Carrier (5), Battleship (4), Destroyer (3), Submarine (3), Patrol Boat (2).
3. Allow placement horizontally or vertically; reject diagonal, overlapping, or out-of-bounds placements.
4. Keep each player's ship locations hidden from the opponent.

Acceptance criteria (verifiable):

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