Add mock API and reorg code for clarity

package.json

@@ -15,6 +15,7 @@
   "dependencies": {
     "@adxp/auth": "*",
     "@adxp/common": "*",
+    "@adxp/mock-api": "git+ssh://git@github.com:bluesky-social/adx-mock-api.git#dc669c19d46b6b98dd692f493276303667670502",
     "@react-native-async-storage/async-storage": "^1.17.6",
     "@react-navigation/bottom-tabs": "^6.3.1",
     "@react-navigation/native": "^6.0.10",
@@ -32,6 +33,7 @@
     "react-native-inappbrowser-reborn": "^3.6.3",
     "react-native-safe-area-context": "^4.3.1",
     "react-native-screens": "^3.13.1",
+    "react-native-url-polyfill": "^1.3.0",
     "react-native-web": "^0.17.7",
     "ucans": "0.9.1"
   },