fix: prevent multiple P2 actions on same offer and improve UI consistency

- Add server validation to prevent P2 from taking multiple actions on the same offer
- Hide P2 action buttons after an action is taken (using \!state.p2Action condition)
- Add offer details display to G3, G4, and G5 (was missing)
- Fix G2 to show offer details instead of just 'Oferta activa'
- Reset game status to PLAYING when changing variant from FINISHED state
- Ensure P2 can only make one decision per offer in all variants

server/src/rooms/GameRoom.ts

@@ -85,6 +85,10 @@ export class GameRoom extends Room<GameState> {
       const player = this.state.players.get(client.sessionId);
       if (!player) return;
       if (player.role !== "P2") return;
+      
+      // Prevent multiple actions on the same offer
+      if (this.state.p2Action) return;
+      
       this.state.p2Action = action; // accept | reject | snatch
       this.resolveP2Action();