build: bump to 4.5.9 (versionCode 466)

The v4.5.8 tag was already published against the version-bump commit alone, so
the twelve commits of actual work had no release to land in - moving the tag made
the CI job fail on an existing release rather than replacing it. A new version
number is the right way round, per the project's own rule against re-cutting a
tag.

Release notes are unchanged: the five locales already describe exactly what these
commits contain.

gradle/libs.versions.toml

@@ -1,8 +1,8 @@
 [versions]
 #noinspection UnusedVersionCatalogEntry
-appVersionCode = "465"
+appVersionCode = "466"
 #noinspection UnusedVersionCatalogEntry
-appVersionName = "4.5.8"
+appVersionName = "4.5.9"
 #noinspection UnusedVersionCatalogEntry
 compileSdk = "37"
 #noinspection UnusedVersionCatalogEntry