Local-first sync: on-device store + offline mutation queue, idempotent server upserts

Screens render synchronously from an AsyncStorage-backed store; every
mutation applies locally and drains to the API in the background
(last-write-wins, client-generated UUIDs). Sydney round-trips are off the
interaction path and the app works fully offline.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/package-lock.json

@@ -12,6 +12,7 @@
         "@react-native-async-storage/async-storage": "2.2.0",
         "expo": "~57.0.11",
         "expo-constants": "~57.0.9",
+        "expo-crypto": "~57.0.1",
         "expo-device": "~57.0.1",
         "expo-font": "~57.0.1",
         "expo-glass-effect": "~57.0.1",
@@ -3713,6 +3714,15 @@
         "react-native": "*"
       }
     },
+    "node_modules/expo-crypto": {
+      "version": "57.0.1",
+      "resolved": "https://registry.npmjs.org/expo-crypto/-/expo-crypto-57.0.1.tgz",
+      "integrity": "sha512-xwegXQw3ATgeL1ZuqbSNrGzOeG+zNeh6Z6DSJk825Qpa3TEQQ1kG3ioE1p3g/SNF373BAVz2iBKUTSytlIbBRA==",
+      "license": "MIT",
+      "peerDependencies": {
+        "expo": "*"
+      }
+    },
     "node_modules/expo-device": {
       "version": "57.0.1",
       "resolved": "https://registry.npmjs.org/expo-device/-/expo-device-57.0.1.tgz",