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/i18n/en.i18n.json

@@ -6,7 +6,8 @@
     "save": "Save",
     "cancel": "Cancel",
     "delete": "Delete",
-    "edit": "Edit"
+    "edit": "Edit",
+    "type": "Type"
   },
   "inventory": {
     "title": "Inventory",
@@ -54,26 +55,38 @@
   "addLot": {
     "title": "Add lot",
     "year": "Harvest year",
-    "quantity": "Quantity"
+    "quantity": "How much?",
+    "amount": "Amount"
   },
-  "quantityKind": {
+  "lotType": {
+    "seed": "Seeds",
+    "plant": "Plants"
+  },
+  "unit": {
     "aFew": "a few",
     "some": "some",
     "plenty": "plenty",
-    "handful": "a handful",
     "pinch": "a pinch",
-    "jar": "a jar",
-    "packet": "a packet",
-    "cob": "a cob",
-    "head": "a head",
-    "pod": "a pod",
-    "ear": "an ear",
-    "fruit": "a fruit",
-    "bulb": "a bulb",
-    "tuber": "a tuber",
-    "seedHead": "a seed head",
-    "bunch": "a bunch",
-    "grams": "grams",
-    "count": "count"
+    "handful": { "singular": "handful", "plural": "handfuls" },
+    "teaspoon": { "singular": "teaspoon", "plural": "teaspoons" },
+    "spoon": { "singular": "spoon", "plural": "spoons" },
+    "cup": { "singular": "cup", "plural": "cups" },
+    "jar": { "singular": "jar", "plural": "jars" },
+    "sack": { "singular": "sack", "plural": "sacks" },
+    "packet": { "singular": "packet", "plural": "packets" },
+    "cob": { "singular": "cob", "plural": "cobs" },
+    "pod": { "singular": "pod", "plural": "pods" },
+    "ear": { "singular": "ear", "plural": "ears" },
+    "head": { "singular": "head", "plural": "heads" },
+    "fruit": { "singular": "fruit", "plural": "fruits" },
+    "bulb": { "singular": "bulb", "plural": "bulbs" },
+    "tuber": { "singular": "tuber", "plural": "tubers" },
+    "seedHead": { "singular": "seed head", "plural": "seed heads" },
+    "bunch": { "singular": "bunch", "plural": "bunches" },
+    "plant": { "singular": "plant", "plural": "plants" },
+    "pot": { "singular": "pot", "plural": "pots" },
+    "tray": { "singular": "tray", "plural": "trays" },
+    "grams": { "singular": "gram", "plural": "grams" },
+    "count": { "singular": "seed", "plural": "seeds" }
   }
 }