feat: add subscription search/sort, rewrite README, upgrade infrastructure

- Subscription list: search by name (case-insensitive), sort by latest
  update / name A-Z / name Z-A / unread count, preference persisted
- README: add build instructions, changelog, reorganize sections
- Upgrade Flutter SDK, Gradle/AGP/Kotlin, migrate to Dart null safety
- Bundle built-in font assets (OpenSans/Roboto/SourceSerif)
- Rename Android package to icu.cytrogen.fluent_reader
- Add i18n strings for sort/search across all 9 locales

Merge pull request #77 from Alkarex/patch-1

FreshRSS using Google Reader API

FreshRSS using Google Reader API

FreshRSS works best through the Google Reader API (more powerful than the Fever API, which is also supported)

Update README.md

add app store link

add beta download links

Update README.md

initial commit