feat: add character sales tracking with 12h countdown timer

- New page /ventas to track characters selling items
- Default 12h duration per character sale
- Real-time countdown with color-coded badges (green/yellow/red/gray)
- Sound alert toggle when sales expire
- CRUD API: GET/POST/DELETE /api/sales
- Flyway migration V2 for character_sales table
- Private per-user (same user sees only their own characters)
- Expired sales remain visible with 'Expirado' badge until manually deleted

src/main/java/com/l2/shots/sales/CharacterSale.java

@@ -0,0 +1,36 @@
+package com.l2.shots.sales;
+
+import io.quarkus.hibernate.orm.panache.PanacheEntityBase;
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Index;
+import jakarta.persistence.Table;
+
+import java.time.Instant;
+import java.util.UUID;
+
+@Entity
+@Table(name = "character_sales", indexes = {
+        @Index(name = "idx_char_sales_user", columnList = "user_id, started_at")
+})
+public class CharacterSale extends PanacheEntityBase {
+
+    @Id
+    public UUID id;
+
+    @Column(name = "user_id", nullable = false)
+    public UUID userId;
+
+    @Column(name = "character_name", nullable = false, length = 50)
+    public String characterName;
+
+    @Column(name = "items_description", nullable = false, columnDefinition = "TEXT")
+    public String itemsDescription;
+
+    @Column(name = "started_at", nullable = false)
+    public Instant startedAt;
+
+    @Column(name = "created_at", nullable = false)
+    public Instant createdAt;
+}