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/build.gradle.kts

@@ -16,11 +16,11 @@ val keystoreProperties = Properties().apply {
 }
 
 android {
-    namespace = "de.jeanlucmakiola.floret"
+    namespace = "de.jeanlucmakiola.agendula"
     compileSdk = 37
 
     defaultConfig {
-        applicationId = "de.jeanlucmakiola.floret"
+        applicationId = "de.jeanlucmakiola.agendula"
         minSdk = 29
         targetSdk = 36
         // The git tag is the single source of truth for released builds: at