feat(inventory): informal quantity scale (number + unit) + seed/plant lots

Rework quantities the way seeds are actually described — a number of an informal
unit — and let a lot hold seeds or plants (plantel).

Quantity model (commons_core):
- Quantity is now { kind, count?, label } — "3 cobs", "2 packets", "a few".
  Count is optional; uncountable vibes (a few, some, pinch) carry no number.
- QuantityKind reorganised into an ascending scale: vibes → containers
  (teaspoon/spoon/cup/jar/sack) → seed & fruit forms → plant units, each tagged
  countable/not. Stored by name; count reuses the existing numeric column.

Lot type (schema v2):
- Lots gain a `type` (seed | plant); germination stays meaningful for seeds.
  schemaVersion 2 with a from1To2 migration (adds the column), drift_schema_v2
  exported, migration test covers v1→v2.

UI:
- New QuantityPicker: a horizontal scale of large seed-glyph icons + a number
  stepper (shown only for countable units), plus a seed/plant SegmentedButton.
  Used in quick-add and add-lot. Lot lines render "3 cobs" / "a few".
- i18n: unit singular/plural (ES/EN, Weblate-friendly), lot-type labels.

Build: slang moved to its CLI (disabled in build_runner to avoid a multi-file
collision); CI runs `dart run slang` before build_runner. 38 tests green,
Linux migrates the existing v1 DB and runs.

apps/app_seeds/lib/ui/variety_detail_screen.dart

@@ -4,11 +4,13 @@ import 'package:flutter_bloc/flutter_bloc.dart';
 
 import '../data/species_repository.dart';
 import '../data/variety_repository.dart';
+import '../db/enums.dart';
 import '../i18n/strings.g.dart';
 import '../state/variety_detail_cubit.dart';
+import 'quantity_kind_l10n.dart';
+import 'quantity_picker.dart';
 import 'seed_glyph.dart';
 import 'theme.dart';
-import 'quantity_kind_l10n.dart';
 
 /// Read + edit view of a single variety: its photo, category, notes, other
 /// names and lots. Edits go through [VarietyDetailCubit]; the view is reactive.
@@ -144,20 +146,11 @@ String _lotSubtitle(Translations t, VarietyLot lot) {
       t.detail.year(year: lot.harvestYear!)
     else
       t.detail.noYear,
-    if (lot.quantity != null) _quantityLabel(t, lot.quantity!),
+    if (lot.quantity != null) quantityDisplay(t, lot.quantity!),
   ];
   return parts.join(' · ');
 }
 
-String _quantityLabel(Translations t, Quantity q) {
-  final kind = quantityKindLabel(t, q.kind);
-  if (q.precise != null) return '${_trimDouble(q.precise!)} $kind';
-  return kind;
-}
-
-String _trimDouble(double v) =>
-    v == v.roundToDouble() ? v.toStringAsFixed(0) : v.toString();
-
 String _germinationPercent(Translations t, double rate) =>
     t.germination.result(percent: (rate * 100).round());
 
@@ -485,7 +478,8 @@ class _EditVarietySheetState extends State<_EditVarietySheet> {
 Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
   final t = context.t;
   final yearController = TextEditingController();
-  QuantityKind? selectedKind;
+  var selectedType = LotType.seed;
+  Quantity? selectedQuantity;
   return showModalBottomSheet<void>(
     context: context,
     isScrollControlled: true,
@@ -506,6 +500,14 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
               style: Theme.of(sheetContext).textTheme.titleLarge,
             ),
             const SizedBox(height: 12),
+            LotTypeSelector(
+              value: selectedType,
+              onChanged: (type) => setState(() {
+                selectedType = type;
+                selectedQuantity = null;
+              }),
+            ),
+            const SizedBox(height: 12),
             TextField(
               key: const Key('addLot.year'),
               controller: yearController,
@@ -521,17 +523,10 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
               style: Theme.of(sheetContext).textTheme.labelLarge,
             ),
             const SizedBox(height: 8),
-            Wrap(
-              spacing: 8,
-              children: [
-                for (final kind in _addLotKinds)
-                  ChoiceChip(
-                    avatar: QuantityKindIcon(kind, size: 18),
-                    label: Text(quantityKindLabel(t, kind)),
-                    selected: selectedKind == kind,
-                    onSelected: (_) => setState(() => selectedKind = kind),
-                  ),
-              ],
+            QuantityPicker(
+              type: selectedType,
+              value: selectedQuantity,
+              onChanged: (q) => selectedQuantity = q,
             ),
             const SizedBox(height: 16),
             Row(
@@ -545,10 +540,9 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
                   key: const Key('addLot.save'),
                   onPressed: () {
                     cubit.addLot(
+                      type: selectedType,
                       year: int.tryParse(yearController.text.trim()),
-                      quantity: selectedKind == null
-                          ? null
-                          : Quantity(kind: selectedKind!),
+                      quantity: selectedQuantity,
                     );
                     Navigator.of(sheetContext).pop();
                   },
@@ -563,15 +557,6 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
   );
 }
 
-const _addLotKinds = <QuantityKind>[
-  QuantityKind.aFew,
-  QuantityKind.handful,
-  QuantityKind.packet,
-  QuantityKind.pod,
-  QuantityKind.cob,
-  QuantityKind.grams,
-];
-
 String? _nullIfBlank(String value) {
   final trimmed = value.trim();
   return trimmed.isEmpty ? null : trimmed;