fix: update service letter seed with realistic dates for chart trends

- Added 5 service letters with createdAt dates spread across 6 months
- Changed from upsert to update/create pattern to allow createdAt modification
- This ensures chart-surat.tsx displays proper trend data
- Previous data had all timestamps at seed time, causing empty 6-month trend

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

.qwen/settings.json

@@ -0,0 +1,7 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(bun *)"
+    ]
+  }
+}