chore(firebase): merge rules into firebase.json

Author: r-park

firebase.json

@@ -1,6 +1,13 @@
 {
   "database": {
-    "rules": "firebase.rules.json"
+    "rules": {
+      "tasks": {
+        "$uid": {
+          ".read": "auth !== null && auth.uid === $uid",
+          ".write": "auth !== null && auth.uid === $uid"
+        }
+      }
+    }
   },
 
   "hosting": {