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/state/variety_detail_cubit.dart

@@ -5,6 +5,7 @@ import 'package:equatable/equatable.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 
 import '../data/variety_repository.dart';
+import '../db/enums.dart';
 
 class VarietyDetailState extends Equatable {
   const VarietyDetailState({
@@ -50,8 +51,16 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
         notes: notes,
       );
 
-  Future<void> addLot({int? year, Quantity? quantity}) =>
-      _repo.addLot(varietyId: varietyId, harvestYear: year, quantity: quantity);
+  Future<void> addLot({
+    LotType type = LotType.seed,
+    int? year,
+    Quantity? quantity,
+  }) => _repo.addLot(
+    varietyId: varietyId,
+    type: type,
+    harvestYear: year,
+    quantity: quantity,
+  );
 
   Future<void> linkSpecies(String speciesId) =>
       _repo.linkSpecies(varietyId, speciesId);