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/it/common.json

@@ -41,6 +41,7 @@
     "webSearch": "Ricerca nel Web",
     "regenerate": "Rigenera",
     "edit": "Modifica",
+    "delete": "Elimina",
     "saveAndSubmit": "Salva e Invia",
     "editMessage": {
         "placeholder": "Scrivi un messaggio..."
@@ -101,5 +102,14 @@
         "translate": "Tradurre"
     },
     "citations": "Citazioni",
-    "downloadCode": "Scarica Codice"
+    "downloadCode": "Scarica Codice",
+    "date": {
+        "pinned": "Fissato",
+        "today": "Oggi",
+        "yesterday": "Ieri",
+        "last7Days": "Ultimi 7 Giorni",
+        "older": "Più Vecchi"
+    },
+    "pin": "Fissa",
+    "unpin": "Rimuovi"
 }