Rename app Floret → Agendula

Floret is promoted to the family / design-language (shared-kit) name; the
tasks app itself becomes Agendula (de.jeanlucmakiola.agendula) — agenda
('things to be done') + Calendula's -ula, a twin of the Calendula name.

Renames the package, namespace, applicationId, rootProject.name, app_name,
FloretApp/FloretNavHost/FloretTransitions classes, theme, F-Droid metadata
dir, CI artifact name, and docs. The botanical word 'florets' is preserved in
the name-origin prose, which is rewritten to Agendula's etymology. Clean
build + unit tests green.

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

app/src/main/res/xml/locales_config.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!--
-    The languages Floret ships translations for. Single source of truth: each
+    The languages Agendula ships translations for. Single source of truth: each
     entry needs a matching res/values-<tag>/strings.xml, and is surfaced in both
     the in-app language picker (parsed at runtime by AppLanguage) and the system
     per-app language settings (Android 13+, via android:localeConfig). To add a