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

feat: enhance custom font upload with WebView rendering, WOFF/WOFF2 support, preview & deletion

- Fix core bug: custom fonts now actually render in article WebView via
  @font-face injection and Jaguar local server font serving route
- Also fix built-in fonts (OpenSans/Roboto/SourceSerif) not rendering in WebView
- Add WOFF/WOFF2 format support for font upload
- Add font preview text in font picker and selected font indicator
- Add custom font deletion UI with confirmation dialog
- Add font file size validation (1KB-50MB)
- Update CSP to allow font-src from local server
- Add missing i18n translations for all 9 locales (zh, de, es, fr, hr, pt, tr, uk)
- Update Android build configuration and dependencies

update packages and use uri for http

add error messages

add semantic labels

add text input types

add customizable text scale

use jaguar to serve resources

add splash screens

switch to third party webview

initial commit