fix: improve Settings page error message for MarkBase config failures

- loadSettings now shows detailed error from MarkBase response body
- MarkBase /api/v2/config returns 500 when config file is incomplete
- Error message now includes actual error details instead of just HTTP status

src/views/AdminView.vue

@@ -1037,7 +1037,11 @@ async function loadSettings() {
   saveMessage.value = ''
   try {
     const resp = await fetch(`${markbaseUrl.value}/api/v2/config`)
-    if (!resp.ok) throw new Error(`HTTP ${resp.status}`)
+    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 cfg = await resp.json()
     uploadPath.value = cfg.server?.upload_path || ''
   } catch (e: any) {