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/db/database.dart

@@ -27,12 +27,16 @@ class AppDatabase extends _$AppDatabase {
   AppDatabase(super.e);
 
   @override
-  int get schemaVersion => 1;
+  int get schemaVersion => 2;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
     onCreate: (m) async => m.createAll(),
-    // Step-by-step upgrades (from1To2, …) are generated into
-    // schema_versions.dart when schemaVersion is bumped. See data-model §5.
+    onUpgrade: (m, from, to) async {
+      // v2: lots can hold seeds or plants/seedlings (plantel).
+      if (from < 2) {
+        await m.addColumn(lots, lots.type);
+      }
+    },
   );
 }