feat(translations): add "Help translate" link to the Weblate engage page

Invite community translations: a new Settings > Help translate row (next to
App language) opens the project's Weblate engage page, plus a Translations
section in the README. Documented in the 2.11.0 changelog.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fastlane/metadata/android/en-US/changelogs/21100.txt

@@ -30,6 +30,9 @@
 - Field icons in the event-form settings. Each optional-field toggle (Settings →
   Event form) now shows the same icon the field uses in the new-event form, so
   the list is easier to scan.
+- Help translate Calendula. A new **Settings → Help translate** link opens the
+  project's Weblate, where you can add or improve a language in your browser — no
+  coding needed. Contributions in any language are welcome.
 
 ### Changed
 - Tidied **Settings → Appearance** into clearer groups (theme & colour, calendar,