components: FullScreenPicker takes an optional actions slot

Forwards a trailing app-bar `actions` lambda through to CollapsingScaffold,
so a full-screen picker can carry a commit/extra action — a custom-value
Add/OK, a Reset — instead of being select-and-dismiss only.

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

CHANGELOG.md

@@ -46,7 +46,9 @@ are no binary releases; "version" tracks the shared `version` in the root build
     `largeTopBar = false` for a pinned single-line bar (the picker variant).
   - `FullScreenPicker` / `OptionPicker` — the full-screen single-select picker,
     now over a pinned single-line bar (a picker is a short list, so no tall
-    collapsing header to scroll past).
+    collapsing header to scroll past). `FullScreenPicker` takes an optional
+    `actions` slot (app-bar trailing items) for pickers that carry a commit or
+    extra action — a custom-value **Add**/**OK**, a **Reset**.
   - `ReorderableColumn` — dependency-free drag-to-reorder for the short, fixed
     grouped-card Settings lists; pairs with `GroupedRow(gapBelow = false)`, which
     hands the column uniform control of row spacing.