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/en-US/description.txt

@@ -0,0 +1,10 @@
+Agendula is a modern, open-source task app for Android. It works directly on an
+existing tasks provider (OpenTasks / tasks.org), so any CalDAV tasks synced to
+your device via DAVx5, SmoothSync or DecSync show up automatically, and changes
+you make sync back the same way — no own account, no own sync.
+
+The differentiator is the design: real Material 3 Expressive throughout, with
+dynamic color, expressive motion, and expressive shapes. Sibling to Calendula.
+
+Privacy: zero telemetry, no analytics, no network access of its own — your data
+never leaves the device except through the sync app you already trust.