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.

pubspec.lock

@@ -644,6 +644,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.13.0"
+  material_symbols_icons:
+    dependency: transitive
+    description:
+      name: material_symbols_icons
+      sha256: "49c532dd0b74544e9d8d93ec0f821d52ec532e7c9263c889ebe71b1be4f34ba7"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.2951.0"
   meta:
     dependency: transitive
     description: