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/CharacterSaleIn.java

@@ -0,0 +1,27 @@
+package com.l2.shots.sales;
+
+import io.quarkus.runtime.annotations.RegisterForReflection;
+
+import java.time.Instant;
+
+@RegisterForReflection
+public record CharacterSaleIn(
+        String characterName,
+        String itemsDescription,
+        Instant startedAt) {
+
+    public CharacterSaleIn {
+        if (characterName == null || characterName.isBlank()) {
+            throw new IllegalArgumentException("characterName is required");
+        }
+        if (characterName.length() > 50) {
+            throw new IllegalArgumentException("characterName must be 50 chars or less");
+        }
+        if (itemsDescription == null || itemsDescription.isBlank()) {
+            throw new IllegalArgumentException("itemsDescription is required");
+        }
+        if (itemsDescription.length() > 2000) {
+            throw new IllegalArgumentException("itemsDescription must be 2000 chars or less");
+        }
+    }
+}