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/seed_glyph.dart

@@ -46,9 +46,13 @@ String? seedGlyphForKind(QuantityKind kind) => switch (kind) {
   QuantityKind.aFew => SeedGlyphs.scattered,
   QuantityKind.some => SeedGlyphs.smallSpoon,
   QuantityKind.plenty => SeedGlyphs.jars,
-  QuantityKind.handful => SeedGlyphs.bigSpoon,
   QuantityKind.pinch => SeedGlyphs.scattered,
+  QuantityKind.handful => SeedGlyphs.bigSpoon,
+  QuantityKind.teaspoon => SeedGlyphs.smallSpoon,
+  QuantityKind.spoon => SeedGlyphs.bigSpoon,
+  QuantityKind.cup => SeedGlyphs.mug,
   QuantityKind.jar => SeedGlyphs.jar,
+  QuantityKind.sack => SeedGlyphs.sack,
   QuantityKind.packet => SeedGlyphs.envelope,
   _ => null,
 };
@@ -59,6 +63,9 @@ IconData _materialIconForKind(QuantityKind kind) => switch (kind) {
   QuantityKind.cob || QuantityKind.ear => Icons.grass,
   QuantityKind.head || QuantityKind.seedHead => Icons.filter_vintage_outlined,
   QuantityKind.fruit => Icons.local_florist_outlined,
+  QuantityKind.plant => Icons.local_florist_outlined,
+  QuantityKind.pot => Icons.yard_outlined,
+  QuantityKind.tray => Icons.grid_on_outlined,
   QuantityKind.bulb ||
   QuantityKind.tuber ||
   QuantityKind.bunch => Icons.spa_outlined,