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

As a player I want to fire at grid coordinates and get hit/miss feedback So that I can locate and sink the opponent’s ships.

The system shall:

1. Enforce alternating turns.
2. Let the active player select a target coordinate on the opponent’s grid.
3. Report 'hit' or 'miss' immediately and record the result on both players’ tracking views.
4. Prevent firing at the same coordinate twice.

Acceptance criteria (verifiable):

• 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.