refine(quantity): drop handful, reorder scale, potted-plant icon, year dropdown

Feedback from the running app:
- Remove "handful" from the scale (redundant with spoon); keep the enum value.
- Reorder so "packet" (sobre) follows "spoon" (cuchara).
- Use the Material Symbols potted-plant for the plant lot type and plant unit
  (adds material_symbols_icons).
- Harvest year is now a dropdown of recent years instead of free text.

38 tests green; Linux build runs with the new icon font bundled.

apps/app_seeds/lib/ui/quantity_picker.dart

@@ -1,5 +1,6 @@
 import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
+import 'package:material_symbols_icons/symbols.dart';
 
 import '../db/enums.dart';
 import '../i18n/strings.g.dart';
@@ -8,15 +9,15 @@ import 'seed_glyph.dart';
 import 'theme.dart';
 
 /// Informal seed amounts, ascending: vibes → containers → seed/fruit forms.
+/// ([QuantityKind.handful] is intentionally omitted — it overlaps with spoon.)
 const seedScaleKinds = <QuantityKind>[
   QuantityKind.aFew,
-  QuantityKind.handful,
   QuantityKind.teaspoon,
   QuantityKind.spoon,
+  QuantityKind.packet,
   QuantityKind.cup,
   QuantityKind.jar,
   QuantityKind.sack,
-  QuantityKind.packet,
   QuantityKind.cob,
   QuantityKind.pod,
   QuantityKind.ear,
@@ -61,7 +62,7 @@ class LotTypeSelector extends StatelessWidget {
         ButtonSegment(
           value: LotType.plant,
           label: Text(t.lotType.plant),
-          icon: const Icon(Icons.local_florist_outlined, size: 18),
+          icon: const Icon(Symbols.potted_plant, size: 18),
         ),
       ],
       selected: {value},