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,

apps/app_seeds/lib/ui/category_palette.dart

@@ -11,19 +11,28 @@ class Swatch {
   final Color ink;
 }
 
-/// A small, muted, earthy palette — one low-saturation key, different hues — so
-/// botanical families (categories) are distinguishable at a glance without
-/// shouting over the green brand. Kept calm on purpose (soft fills, legible
-/// ink). Order is stable; new entries append only.
+/// A muted, earthy palette — one low-saturation key, hues spread around the
+/// wheel — so botanical families (categories) are distinguishable at a glance
+/// without shouting over the green brand. Kept calm on purpose (soft fills,
+/// legible ink). 14 tones keep collisions rare for a typical 6–10 family
+/// inventory. Order is stable; new entries append only.
+// Inks are tuned so the label meets WCAG AA (≥4.5:1) on its own fill — see
+// test/ui/category_palette_contrast_test.dart.
 const _familyPalette = <Swatch>[
   Swatch(Color(0xFFE8EEDA), Color(0xFF556B2F)), // olive
-  Swatch(Color(0xFFF3E2D8), Color(0xFF9C5B3B)), // terracotta
-  Swatch(Color(0xFFF3EBD3), Color(0xFF8A6D1E)), // ochre
+  Swatch(Color(0xFFF3E2D8), Color(0xFF8E5336)), // terracotta
+  Swatch(Color(0xFFF3EBD3), Color(0xFF7C621B)), // ochre
   Swatch(Color(0xFFDDEAE6), Color(0xFF3E7168)), // sage teal
-  Swatch(Color(0xFFF0E1E4), Color(0xFF9B5566)), // dusty rose
+  Swatch(Color(0xFFF0E1E4), Color(0xFF8F4E5E)), // dusty rose
   Swatch(Color(0xFFE0E6EE), Color(0xFF4A6489)), // slate blue
   Swatch(Color(0xFFE9E1EE), Color(0xFF6E5090)), // plum
   Swatch(Color(0xFFEBE3D8), Color(0xFF7A5A3A)), // warm brown
+  Swatch(Color(0xFFDCEAD6), Color(0xFF3E6B3A)), // forest green
+  Swatch(Color(0xFFD6E7EA), Color(0xFF2C6A73)), // petrol
+  Swatch(Color(0xFFF3DEDB), Color(0xFFA14234)), // brick red
+  Swatch(Color(0xFFEFDCEA), Color(0xFF864C7C)), // mauve
+  Swatch(Color(0xFFE1E1F1), Color(0xFF4E5199)), // indigo
+  Swatch(Color(0xFFDFE4E9), Color(0xFF4C5E70)), // steel
 ];
 
 /// A stable (launch-to-launch, platform-independent) hash of a category name.
@@ -48,9 +57,9 @@ Swatch categorySwatch(String category) =>
 /// tones for woody/underground ones.
 Swatch lotTypeSwatch(LotType type) => switch (type) {
   LotType.seed => const Swatch(seedPrimaryContainer, seedOnPrimaryContainer),
-  LotType.seedling => const Swatch(Color(0xFFDDEBCF), Color(0xFF4E7A2E)),
-  LotType.plant => const Swatch(Color(0xFFD9EAD9), Color(0xFF2F7D34)),
+  LotType.seedling => const Swatch(Color(0xFFDDEBCF), Color(0xFF456D29)),
+  LotType.plant => const Swatch(Color(0xFFD9EAD9), Color(0xFF2A702F)),
   LotType.tree => const Swatch(Color(0xFFE3D9C8), Color(0xFF6B4F2A)),
-  LotType.bulb => const Swatch(Color(0xFFF3E9CF), Color(0xFF8A6D1E)),
-  LotType.cutting => const Swatch(Color(0xFFE6EAD3), Color(0xFF63702F)),
+  LotType.bulb => const Swatch(Color(0xFFF3E9CF), Color(0xFF7B611B)),
+  LotType.cutting => const Swatch(Color(0xFFE6EAD3), Color(0xFF5D692C)),
 };

apps/app_seeds/test/ui/category_palette_contrast_test.dart

@@ -0,0 +1,38 @@
+import 'dart:math' as math;
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/enums.dart';
+import 'package:tane/ui/category_palette.dart';
+
+/// Chip labels are drawn in [Swatch.ink] over [Swatch.fill]; that pairing must
+/// clear WCAG AA for normal text (≥4.5:1), like the rest of the palette
+/// (see theme_contrast_test.dart). Locks the tuned inks against regressions.
+void main() {
+  double lin(double c) =>
+      c <= 0.03928 ? c / 12.92 : math.pow((c + 0.055) / 1.055, 2.4).toDouble();
+  double luminance(Color c) =>
+      0.2126 * lin(c.r) + 0.7152 * lin(c.g) + 0.0722 * lin(c.b);
+  double contrast(Color a, Color b) {
+    final la = luminance(a), lb = luminance(b);
+    final hi = math.max(la, lb), lo = math.min(la, lb);
+    return (hi + 0.05) / (lo + 0.05);
+  }
+
+  test('every category swatch label meets AA on its fill', () {
+    // Cover the whole palette by probing many distinct category names.
+    for (var i = 0; i < 60; i++) {
+      final s = categorySwatch('family-$i');
+      expect(contrast(s.ink, s.fill), greaterThanOrEqualTo(4.5),
+          reason: 'category-$i ink on fill');
+    }
+  });
+
+  test('every lot-form swatch label meets AA on its fill', () {
+    for (final type in LotType.values) {
+      final s = lotTypeSwatch(type);
+      expect(contrast(s.ink, s.fill), greaterThanOrEqualTo(4.5),
+          reason: '$type ink on fill');
+    }
+  });
+}