components: add CollapsingScaffold + OptionPicker/FullScreenPicker (batch-2)

The family's collapsing settings/sub-screen scaffold and the full-screen
single-select picker built on it (used for theme/list/reminder option dialogs).
Adds material-icons-core (ArrowBack/Check) and a generic 'back' string apps can
override. ReminderFormatting (labels over app-specific R.plurals + per-app
presets) deliberately NOT included — it needs a label-callback API, a separate
pass.

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

components/src/main/res/values/strings.xml

@@ -0,0 +1,7 @@
+<resources>
+    <!--
+      Generic component strings. App-agnostic fallbacks; an app may override any
+      of these with its own (localized) value via resource merge.
+    -->
+    <string name="back">Back</string>
+</resources>