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/ml/knowledge.json

@@ -10,9 +10,6 @@
     "expandedColumns": {
         "name": "നാമം"
     },
-    "tooltip": {
-        "delete": "ഇല്ലാതാക്കുക"
-    },
     "confirm": {
         "delete": "നിങ്ങൾക്ക് ഈ വിജ്ഞാനം ഇല്ലാതാക്കണമെന്ന് ഉറപ്പാണോ?"
     },