Feat: Agregar sistema de alias para chats

- Agregar campo alias a tabla chats con migración 003
- Crear endpoint PUT /api/messages/:instanceId/:chatId/alias
- Modificar MCP para priorizar alias sobre nombres automáticos
- Crear modal ChatAliasModal para editar alias desde UI
- Agregar botón de editar alias en ChatItem
- Integrar modal en página de mensajes

El alias permite asignar nombres personalizados a chats que tienen
prioridad sobre los nombres de WhatsApp tanto en la interfaz como
en el MCP para agentes IA.

server/api/messages/[instanceId]/[chatId]/alias.put.ts

@@ -0,0 +1,68 @@
+/**
+ * PUT /api/messages/:instanceId/:chatId/alias
+ * Update the alias of a chat
+ */
+import { query } from '../../../../utils/database'
+
+export default defineEventHandler(async (event) => {
+  const username = getHeader(event, 'x-authentik-username')
+  if (!username) {
+    throw createError({ statusCode: 401, message: 'Unauthorized' })
+  }
+
+  const instanceId = getRouterParam(event, 'instanceId')
+  const chatId = getRouterParam(event, 'chatId')
+
+  if (!instanceId) {
+    throw createError({ statusCode: 400, message: 'Missing instanceId' })
+  }
+
+  if (!chatId) {
+    throw createError({ statusCode: 400, message: 'Missing chatId' })
+  }
+
+  const body = await readBody<{ alias: string | null }>(event)
+
+  // alias can be null to remove it, or a string to set it
+  if (body?.alias === undefined) {
+    throw createError({ statusCode: 400, message: 'Missing alias in request body' })
+  }
+
+  try {
+    // Update the alias
+    const result = await query(
+      `UPDATE chats
+       SET alias = $1, updated_at = NOW()
+       WHERE id = $2 AND instance_id = $3
+       RETURNING id, jid, name, alias, is_group`,
+      [body.alias || null, chatId, instanceId]
+    )
+
+    if (result.rows.length === 0) {
+      throw createError({ statusCode: 404, message: 'Chat not found' })
+    }
+
+    const chat = result.rows[0]
+    return {
+      success: true,
+      chat: {
+        id: chat.id,
+        jid: chat.jid,
+        name: chat.name,
+        alias: chat.alias,
+        isGroup: chat.is_group
+      }
+    }
+  } catch (error: any) {
+    console.error('[Alias API] Error updating alias:', error)
+
+    if (error.statusCode) {
+      throw error
+    }
+
+    throw createError({
+      statusCode: 500,
+      message: error.message || 'Error updating alias'
+    })
+  }
+})