chore: 1.0.0-beta.1

The first public build. CHANGELOG's Unreleased section is rewritten as
user-facing notes, since it becomes the beta's release notes. The README
gains an install section, and the store short description fits Play's
80 characters.

app/build.gradle.kts

@@ -27,11 +27,13 @@ android {
         // These committed values ARE the source of truth for a release: merging
         // a bumped versionName into main triggers .gitea/workflows/release.yaml,
         // which builds this version and then creates the matching vX.Y.Z tag +
-        // release itself (versionCode is pinned to MAJOR*10000 + MINOR*100 +
-        // PATCH from versionName, e.g. 0.2.0 -> 200). The Gitea release is marked
-        // as a pre-release while MAJOR is 0. See docs/RELEASING.md.
-        versionCode = 100
-        versionName = "0.1.0"
+        // release itself. A versionName of X.Y.Z-beta.N pushed to a release/*
+        // branch instead cuts a Codeberg-only pre-release (beta.yaml).
+        // versionCode is derived from versionName by scripts/version_info.sh
+        // (1.0.0-beta.1 -> 1000001, 1.0.0 -> 1000099), and CI fails if the
+        // committed one doesn't match. See docs/RELEASING.md.
+        versionCode = 1000001
+        versionName = "1.0.0-beta.1"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }