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>

CONTRIBUTING.md

@@ -1,6 +1,6 @@
-# Contributing to Floret
+# Contributing to Agendula
 
-Thanks for your interest in Floret — a Material 3 Expressive task app that's a
+Thanks for your interest in Agendula — a Material 3 Expressive task app that's a
 pure front-end over the OpenTasks `TaskContract` provider, with no own database
 or sync stack. Before diving in, skim [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md)
 (how it's built), [`docs/ROADMAP.md`](docs/ROADMAP.md) (what's next), and
@@ -80,7 +80,7 @@ push, so run these locally before opening a PR. Keep CI green.
 
 ## Scope
 
-Floret stays true to its thesis: a front-end over **open** task backends
+Agendula stays true to its thesis: a front-end over **open** task backends
 (CalDAV / iCalendar / DecSync via the OpenTasks provider). Proprietary backends
 (Google Tasks, Microsoft To Do) are out of scope by design — they'd mean owning
 a sync stack. v1 targets the OpenTasks contract (OpenTasks + tasks.org); jtx's