Word Guesser 2.4 — the leaderboard moves to Firebase

Word Guesser 2.4 — the leaderboard moves to Firebase.

Since 2.3:

• The daily and timed leaderboards now run on a Firebase Realtime Database instead of dreamlo.
  Still REST only — no client SDK, no new runtime dependency — and still scoped per language, per
  day and per word length.
• ⚠️ The old dreamlo scores are gone. They lived on that service and did not come along. This
  is the one thing you lose by updating; the boards start empty and fill up again from today.
• No write key ships any more. The previous version carried the dreamlo write key in the app,
  which meant anyone who extracted it could wipe or forge the board. Authorisation is now entirely
  server-side, in database rules, so there is no key left in the APK to leak. Writes are
  append-only: a submitted score can be added but not overwritten or deleted.
• Cleartext HTTP is now refused outright. dreamlo was the only host that needed it. Everything
  the app talks to is HTTPS, and on Android below API 28 — where cleartext is permitted by
  default — the network security config now denies it explicitly.

Nothing else changed: same gameplay, same 17 languages, same scenic backdrop, same duels.

APK: 103,016 bytes, versionCode 6, minSdk 21 / targetSdk 34, R8 + resource shrinking.
SHA-256: 6f2b40ed660ec25aa7e7af0bbc5af0cda773fe414add831de1ed4bd9f31f5a56
Signing cert SHA-256: f6787964f8e619e59185360034df1ad16de88e13f94a61539e348761cf0e7d63 —
the same key as 1.0, so this installs as an update.

These are the exact bytes on the download page and in the F-Droid repo; the asset here is that same
file, not a rebuild.

Also in the shared hrbons F-Droid repo: https://abons.github.io/wordguesser/fdroid/repo

Still: no ads, no tracking, no billing, no third-party runtime dependencies.