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>

fdroid-metadata/de.jeanlucmakiola.agendula.yml

@@ -0,0 +1,10 @@
+AuthorName: Jean-Luc Makiola
+License: MIT
+Name: Agendula
+Summary: A modern Material 3 Expressive task app for Android.
+
+Categories:
+  - Time
+
+SourceCode: https://gitea.jeanlucmakiola.de/makiolaj/agendula
+IssueTracker: https://gitea.jeanlucmakiola.de/makiolaj/agendula/issues