feat: add pin/unpin functionality to chat history

Adds pin/unpin functionality to the chat history sidebar, allowing users to keep important conversations readily accessible. This improves user experience and helps organize past interactions.

This feature includes:
- Pin/unpin buttons in the chat history sidebar.
- Updated database schema to include `is_pinned` field for chat history items.
- Localized translations for pin/unpin actions.
- Updated UI to display pinned items at the top of the list.

src/assets/locale/fa/common.json

@@ -41,6 +41,7 @@
     "webSearch": "جستجوی وب",
     "regenerate": "ایجاد مجدد",
     "edit": "ویرایش",
+    "delete": "حذف",
     "saveAndSubmit": "ذخیره و ارسال",
     "editMessage": {
         "placeholder": "یک پیام وارد کنید..."
@@ -95,5 +96,14 @@
         "advanced": "تنظیمات بیشتر مدل"
     },
     "citations": "منابع",
-    "downloadCode": "دانلود کد"
+    "downloadCode": "دانلود کد",
+    "date": {
+        "pinned": "پین شده",
+        "today": "امروز",
+        "yesterday": "دیروز",
+        "last7Days": "۷ روز گذشته",
+        "older": "قدیمی‌تر"
+    },
+    "pin": "پین کردن",
+    "unpin": "حذف پین"
 }