feat(ui): align inventory + detail with mockups (seed icons, green theme)

Visual pass toward docs/mockups (06 inventory, 07 item):
- Bundle the seedks icon font (chars a–k → seed pictograms: jar, packet, spoon…)
  and a SeedGlyph/QuantityKindIcon helper.
- Green app bar + pale-green canvas theme (buildTaneTheme).
- Inventory list: rounded-square photo thumbnail or green initial avatar, bold
  title, scientific-name subtitle, trailing edit pencil, styled category
  headers, rounded search field, seed-glyph empty state.
- Quantity selectors (quick-add + add-lot) show the seed pictogram + word;
  detail lot lines use the kind's glyph.
- Detail header restyled to mockup 07: category link + scientific name on the
  left, photo on the right.

watchInventory now also returns the linked species' scientific name (subtitle).
37 app tests green; seedks font verified in the Linux asset bundle.

apps/app_seeds/test/data/variety_detail_test.dart

@@ -83,6 +83,10 @@ void main() {
       final detail = await repo.watchVariety(id).first;
       expect(detail!.scientificName, 'Solanum lycopersicum');
       expect(detail.category, 'Solanaceae'); // prefilled from family
+
+      // The inventory list row also surfaces the scientific name (subtitle).
+      final row = (await repo.watchInventory().first).single;
+      expect(row.scientificName, 'Solanum lycopersicum');
     },
   );