Make Khoj chat a separate Progressive Web App (PWA) for easier access

src/khoj/interface/web/chat.html

@@ -6,7 +6,7 @@
 
         <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 144 144%22><text y=%22.86em%22 font-size=%22144%22>🦅</text></svg>">
         <link rel="icon" type="image/png" sizes="144x144" href="/static/assets/icons/favicon-144x144.png">
-        <link rel="manifest" href="/static/khoj.webmanifest">
+        <link rel="manifest" href="/static/khoj_chat.webmanifest">
     </head>
     <script>
         function formatDate(date) {

src/khoj/interface/web/khoj_chat.webmanifest

@@ -0,0 +1,16 @@
+{
+    "name": "Khoj Chat",
+    "short_name": "Khoj Chat",
+    "description": "A personal assistant for your notes",
+    "icons": [
+        {
+            "src": "/static/assets/icons/favicon-144x144.png",
+            "sizes": "144x144",
+            "type": "image/png"
+        }
+    ],
+    "theme_color": "#ffffff",
+    "background_color": "#ffffff",
+    "display": "standalone",
+    "start_url": "/chat"
+}