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/test/db/migration_test.dart

@@ -11,11 +11,20 @@ void main() {
     verifier = SchemaVerifier(GeneratedHelper());
   });
 
-  test('freshly created database matches the exported schema v1', () async {
-    // Guards that `createAll` stays in sync with drift_schemas/drift_schema_v1.json.
-    final schema = await verifier.schemaAt(1);
+  test('freshly created database matches the exported schema v2', () async {
+    final schema = await verifier.schemaAt(2);
     final db = AppDatabase(schema.newConnection());
-    await verifier.migrateAndValidate(db, 1);
+    await verifier.migrateAndValidate(db, 2);
     await db.close();
   });
+
+  test(
+    'upgrades v1 → v2 (adds Lot.type) and matches the fresh schema',
+    () async {
+      final connection = await verifier.startAt(1);
+      final db = AppDatabase(connection);
+      await verifier.migrateAndValidate(db, 2);
+      await db.close();
+    },
+  );
 }