fix: DbSelector 连接后自动选择第一个有数据的 DB，切换 DB 时重新加载键树

- 新增 getDefaultDb(): 优先恢复 lastDbMap > 第一个有数据的 DB > DB0
- onMounted 执行 DB 选择（覆盖首次连接和右键重连场景）
- activeId watcher 改为完整 DB 选择流程（不再硬编码 DB0）
- isConnected watcher 精简为仅加载自定义名称（避免竞态重复调用）
- switchDb() 新增 scanKeys 重新加载键树

src/renderer/src/components/key/DbSelector.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref, watch, computed } from 'vue'
+import { ref, watch, computed, onMounted } from 'vue'
 import { useConnectionStore } from '@renderer/stores/connection'
 import { useKeyStore } from '@renderer/stores/key'
 import { useI18n } from '@renderer/i18n'
@@ -113,14 +113,36 @@ async function fetchDbInfo() {
   }
 }
 
+// Determine the default DB: saved last DB > first non-empty > 0
+function getDefaultDb(): number {
+  if (!connStore.activeId) return 0
+  // Restore saved DB if exists
+  const saved = connStore.lastDbMap[connStore.activeId]
+  if (saved !== undefined && saved !== null) return saved
+  // Auto-detect: first non-empty DB
+  for (let i = 0; i < dbCount.value; i++) {
+    if ((dbKeyCounts.value[i] ?? 0) > 0) return i
+  }
+  return 0
+}
+
+// Initialize DB selection on mount (covers initial connect and right-click reconnect)
+onMounted(async () => {
+  if (!connStore.isConnected || !connStore.activeId) return
+  loadCustomNames()
+  await fetchDbInfo()
+  const defaultDb = getDefaultDb()
+  selectedDb.value = defaultDb
+  keyStore.currentDb = defaultDb
+  await window.electronAPI.redis.selectDb(connStore.activeId, defaultDb)
+  await keyStore.scanKeys(connStore.activeId, '0', true)
+})
+
 watch(
   () => connStore.isConnected,
-  async (connected) => {
+  (connected) => {
     if (connected) {
-      selectedDb.value = 0
-      keyStore.currentDb = 0
       loadCustomNames()
-      await fetchDbInfo()
     }
   }
 )
@@ -128,12 +150,14 @@ watch(
 watch(
   () => connStore.activeId,
   async () => {
+    if (!connStore.isConnected || !connStore.activeId) return
     loadCustomNames()
-    if (connStore.isConnected) {
-      selectedDb.value = 0
-      keyStore.currentDb = 0
-      await fetchDbInfo()
-    }
+    await fetchDbInfo()
+    const defaultDb = getDefaultDb()
+    selectedDb.value = defaultDb
+    keyStore.currentDb = defaultDb
+    await window.electronAPI.redis.selectDb(connStore.activeId, defaultDb)
+    await keyStore.scanKeys(connStore.activeId, '0', true)
   }
 )
 
@@ -142,6 +166,8 @@ async function switchDb(db: number) {
   selectedDb.value = db
   connStore.saveLastDb(connStore.activeId, db)
   await keyStore.selectDb(connStore.activeId, db)
+  // Reload key tree for the new DB
+  await keyStore.scanKeys(connStore.activeId, '0', true)
 }
 
 function formatCount(n: number): string {