feat(mobile): self-update dialog with verified APK download and install (M5)

Checks the server for a newer release at most every 6 hours and on
demand in Profile, shows release notes, downloads the APK with progress,
verifies SHA-256 in 1 MB chunks and hands it to the system installer.
Updates below min_supported cannot be dismissed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mobile/package.json

@@ -20,12 +20,15 @@
     "expo": "~53.0.20",
     "expo-build-properties": "~0.14.8",
     "expo-constants": "~17.1.7",
+    "expo-file-system": "~18.1.11",
     "expo-font": "~13.3.2",
+    "expo-intent-launcher": "~12.1.5",
     "expo-linking": "~7.1.7",
     "expo-router": "~5.1.11",
     "expo-secure-store": "~14.2.4",
     "expo-status-bar": "~2.2.3",
     "i18next": "^25.2.1",
+    "js-sha256": "^1.0.0",
     "query-string": "^7.1.3",
     "react": "19.0.0",
     "react-i18next": "^15.5.3",