fix: show clear error message when MarkBase needs restart (PostgreSQL→SQLite migration)

- Detects 'missing field postgresql' error from MarkBase config endpoint
- Shows user-friendly message: 'MarkBase needs restart (PostgreSQL→SQLite migration)'
- Helps users understand the error is due to outdated MarkBase instance

src/views/AdminView.vue

@@ -1038,9 +1038,13 @@ async function loadSettings() {
   try {
     const resp = await fetch(`${markbaseUrl.value}/api/v2/config`)
     if (!resp.ok) {
-      // MarkBase config may return 500 if config file is incomplete
       const errData = await resp.json().catch(() => null)
-      throw new Error(`HTTP ${resp.status}: ${errData?.error || resp.statusText}`)
+      const errMsg = errData?.error || resp.statusText || ''
+      // MarkBase config may return 500 if still running old version requiring postgresql
+      if (errMsg.includes('postgresql')) {
+        throw new Error('MarkBase needs restart (PostgreSQL→SQLite migration)')
+      }
+      throw new Error(`HTTP ${resp.status}: ${errMsg}`)
     }
     const cfg = await resp.json()
     uploadPath.value = cfg.server?.upload_path || ''