polish(ux): AA-contrast chip inks, 14-tone palette, calendar month auto-scroll

Blind-build polish pass over the recent sales/chips/calendar work:

- Chip label contrast: 7 palette inks (terracotta, ochre, rose, seedling,
  plant, bulb, cutting) sat below WCAG AA on their own fill; darkened
  (hue preserved) to ≥4.8:1. New category_palette_contrast_test locks it.
- Palette expanded 8 → 14 earthy tones (hues spread around the wheel) so
  family colours rarely collide for a typical 6–10 family inventory,
  keeping the stable-by-name, cross-screen-consistent scheme. Every new
  ink meets AA on its fill.
- Calendar month strip now actually scrolls the selected month into view
  (the comment promised it but it was never wired) — late-year months are
  no longer left off-screen when the screen opens.
- Minor: dead code removed from the month chip.

dart analyze clean; palette/contrast/calendar/quantity/overflow/inventory
suites green.

apps/app_seeds/lib/ui/calendar_screen.dart

@@ -102,13 +102,43 @@ class _CalendarScreenState extends State<CalendarScreen> {
 }
 
 /// A horizontally scrolling strip of the twelve months; the picked one is
-/// filled. Scrolls the picked month into view on first build.
-class _MonthStrip extends StatelessWidget {
+/// filled. Scrolls the picked month into view (so late-year months aren't left
+/// off-screen when the screen opens in, say, November).
+class _MonthStrip extends StatefulWidget {
   const _MonthStrip({required this.month, required this.onSelect});
 
   final int month;
   final ValueChanged<int> onSelect;
 
+  @override
+  State<_MonthStrip> createState() => _MonthStripState();
+}
+
+class _MonthStripState extends State<_MonthStrip> {
+  final _selectedKey = GlobalKey();
+
+  @override
+  void initState() {
+    super.initState();
+    _revealSelected();
+  }
+
+  @override
+  void didUpdateWidget(_MonthStrip old) {
+    super.didUpdateWidget(old);
+    if (old.month != widget.month) _revealSelected();
+  }
+
+  void _revealSelected() {
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      final ctx = _selectedKey.currentContext;
+      if (ctx != null) {
+        Scrollable.ensureVisible(ctx,
+            alignment: 0.5, duration: const Duration(milliseconds: 250));
+      }
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     final locale = materialLocaleFor(Localizations.localeOf(context));
@@ -122,12 +152,16 @@ class _MonthStrip extends StatelessWidget {
         separatorBuilder: (_, _) => const SizedBox(width: 8),
         itemBuilder: (context, i) {
           final m = i + 1;
-          final selected = m == month;
+          final selected = m == widget.month;
           return ChoiceChip(
             key: Key('calendar.month.$m'),
-            label: Text(_capitalise(fmt.format(DateTime(2000, m)))),
+            labelPadding: const EdgeInsets.symmetric(horizontal: 6),
+            label: Text(
+              _capitalise(fmt.format(DateTime(2000, m))),
+              key: selected ? _selectedKey : null,
+            ),
             selected: selected,
-            onSelected: (_) => onSelect(m),
+            onSelected: (_) => widget.onSelect(m),
             selectedColor: seedPrimaryContainer,
             labelStyle: TextStyle(
               color: selected ? seedOnPrimaryContainer : seedMuted,