feat(components): expose SelectedCheck as a family primitive

The trailing check that marks a chosen row in a full-screen picker was
private to OptionPicker, so every consumer hand-rolled its own copy.
Calendula alone carried five, and they had drifted: the kit drew
Icons.Rounded.Check, all five app copies drew Icons.Default.Check.

Make it public with KDoc so pickers share one selection affordance
instead of re-deriving it. Rounded wins, as the kit's existing choice.

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

components/src/main/kotlin/de/jeanlucmakiola/floret/components/OptionPicker.kt

@@ -102,8 +102,18 @@ fun <T> OptionPicker(
     }
 }
 
+/**
+ * The trailing check that marks the chosen row in a full-screen picker — the
+ * family's single selection affordance, so every picker (option, reminder,
+ * agenda range, timezone, calendar, recurrence) marks its selection the same
+ * way. Pair it with `GroupedRow(selected = true)`: the tonal highlight carries
+ * the state at a glance, the check confirms it unambiguously.
+ *
+ * Purely decorative — the row itself owns the semantics, so it takes no
+ * content description.
+ */
 @Composable
-private fun SelectedCheck() {
+fun SelectedCheck() {
     Icon(
         imageVector = Icons.Rounded.Check,
         contentDescription = null,