feat(ux): usable amounts, colour-coded category/form chips, currency quick-picks

Four usability passes across the everyday flows:

- Quantity picker: a countable unit (cob/pod/ear…) now defaults to 1 and
  the stepper clamps at a minimum of 1 — you can never store 'a cob' with
  a blank/zero figure. Vibe units (a few) still carry no number.
- Category & form chips are colour-coded (new category_palette.dart): a
  small muted earthy palette maps each botanical family to a STABLE
  tonality (fill + readable ink), and each lot form gets its own tone.
  Applied to the inventory filter bar (now grouped attributes | forms |
  families, separated by a hairline), the list's category headers (a
  matching colour dot), and the lot-form selector.
- Sale currency: quick-pick chips (€ · Ğ1 · hours) fill the field in one
  tap — Ğ1 offered quietly among familiar options, never imposed — while
  free text still takes anything else. New i18n key sale.hours (en/es/pt/ast).

Tests: quantity_picker_test (default-1, clamp, vibe, clear-still-1),
category_palette_test (stable/distinct swatches); overflow guard + the
inventory widget tests stay green.

apps/app_seeds/test/ui/category_palette_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/enums.dart';
+import 'package:tane/ui/category_palette.dart';
+
+/// Category/form colours must be STABLE (same name → same tonality every
+/// launch) so a family's chip and list header always match.
+void main() {
+  test('a category always maps to the same swatch', () {
+    final a = categorySwatch('Solanáceas');
+    final b = categorySwatch('Solanáceas');
+    expect(a.fill, b.fill);
+    expect(a.ink, b.ink);
+  });
+
+  test('different families generally get different tonalities', () {
+    final names = [
+      'Solanáceas',
+      'Leguminosas',
+      'Cucurbitáceas',
+      'Brasicáceas',
+      'Asteráceas',
+      'Amarantáceas',
+    ];
+    final inks = {for (final n in names) categorySwatch(n).ink};
+    // Not required to be all-distinct (palette wraps), but a fixed input set
+    // must not collapse to a single colour.
+    expect(inks.length, greaterThan(1));
+  });
+
+  test('every lot form has its own swatch', () {
+    for (final type in LotType.values) {
+      final s = lotTypeSwatch(type);
+      expect(s.fill, isNotNull);
+      expect(s.ink, isNotNull);
+    }
+  });
+}

apps/app_seeds/test/ui/quantity_picker_test.dart

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+import 'package:commons_core/commons_core.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/enums.dart';
+import 'package:tane/ui/quantity_picker.dart';
+
+import '../support/test_support.dart';
+
+/// A countable amount must never be blank: picking cob/pod/… defaults to 1 and
+/// the stepper can't drop below 1 — you can't save "a cob" with no figure.
+void main() {
+  Quantity? emitted;
+
+  Future<void> pumpPicker(WidgetTester tester,
+      {LotType type = LotType.seed}) async {
+    emitted = null;
+    final db = newTestDatabase();
+    addTearDown(db.close);
+    await tester.pumpWidget(wrapScreen(
+      repository: newTestRepository(db),
+      child: Scaffold(
+        body: QuantityPicker(
+          type: type,
+          onChanged: (q) => emitted = q,
+        ),
+      ),
+    ));
+    await tester.pump();
+  }
+
+  testWidgets('selecting a countable unit defaults the count to 1',
+      (tester) async {
+    await pumpPicker(tester);
+    await tester.tap(find.byKey(const Key('quantity.kind.cob')));
+    await tester.pump();
+
+    expect(emitted, isNotNull);
+    expect(emitted!.kind, QuantityKind.cob);
+    expect(emitted!.count, 1);
+    expect(
+      find.widgetWithText(TextField, '1'),
+      findsOneWidget,
+      reason: 'the count field shows 1, not an empty box',
+    );
+  });
+
+  testWidgets('the minus button never takes a countable amount below 1',
+      (tester) async {
+    await pumpPicker(tester);
+    await tester.tap(find.byKey(const Key('quantity.kind.cob')));
+    await tester.pump();
+    // Two decrements from 1 must clamp at 1, never 0 or blank.
+    await tester.tap(find.byIcon(Icons.remove));
+    await tester.pump();
+    await tester.tap(find.byIcon(Icons.remove));
+    await tester.pump();
+
+    expect(emitted!.count, 1);
+  });
+
+  testWidgets('a vibe unit (a few) carries no number and shows no stepper',
+      (tester) async {
+    await pumpPicker(tester);
+    await tester.tap(find.byKey(const Key('quantity.kind.aFew')));
+    await tester.pump();
+
+    expect(emitted!.kind, QuantityKind.aFew);
+    expect(emitted!.count, isNull);
+    expect(find.byKey(const Key('quantity.count')), findsNothing);
+  });
+
+  testWidgets('typing then clearing the box still stores 1, never empty',
+      (tester) async {
+    await pumpPicker(tester);
+    await tester.tap(find.byKey(const Key('quantity.kind.pod')));
+    await tester.pump();
+    await tester.enterText(find.byKey(const Key('quantity.count')), '');
+    await tester.pump();
+
+    expect(emitted!.kind, QuantityKind.pod);
+    expect(emitted!.count, 1);
+  });
+}