Feature: Cargar historial de WhatsApp desde la UI

- Agregar endpoint oldest.get.ts para obtener mensaje mas antiguo de un chat
- Agregar boton 'Cargar historial de WhatsApp' en vista de mensajes
- Mejorar HistorySection.vue con selector de chats y auto-deteccion

server/api/messages/[instanceId]/[chatId]/oldest.get.ts

@@ -0,0 +1,65 @@
+/**
+ * GET /api/messages/:instanceId/:chatId/oldest
+ * Get the oldest message from a chat for use with fetchMessageHistory
+ */
+import { query } from '../../../../utils/database'
+
+interface ChatRow {
+  jid: string
+}
+
+interface MessageRow {
+  message_id: string
+  from_me: boolean
+  timestamp: Date
+}
+
+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')
+
+  // Get chat info (jid)
+  const chatResult = await query<ChatRow>(
+    'SELECT jid FROM chats WHERE id = $1 AND instance_id = $2',
+    [chatId, instanceId]
+  )
+
+  if (!chatResult.rows.length) {
+    throw createError({ statusCode: 404, message: 'Chat not found' })
+  }
+
+  // Get oldest message
+  const oldestResult = await query<MessageRow>(
+    `SELECT message_id, from_me, timestamp
+     FROM messages
+     WHERE chat_id = $1
+     ORDER BY timestamp ASC
+     LIMIT 1`,
+    [chatId]
+  )
+
+  if (!oldestResult.rows.length) {
+    return {
+      hasMessages: false,
+      messageKey: null,
+      timestamp: null
+    }
+  }
+
+  const oldest = oldestResult.rows[0]
+
+  return {
+    hasMessages: true,
+    messageKey: {
+      remoteJid: chatResult.rows[0].jid,
+      id: oldest.message_id,
+      fromMe: oldest.from_me
+    },
+    timestamp: Math.floor(new Date(oldest.timestamp).getTime() / 1000)
+  }
+})