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/lib/ui/theme.dart

@@ -0,0 +1,35 @@
+import 'package:flutter/material.dart';
+
+/// Seed-green palette drawn from the mockups (docs/mockups): a green app bar and
+/// a pale-green canvas.
+const seedGreen = Color(0xFF3C8B2E);
+const seedGreenDark = Color(0xFF1B5E20);
+const seedCanvas = Color(0xFFEAF4E2);
+const seedLink = Color(0xFF1E88C0);
+
+ThemeData buildTaneTheme() {
+  final scheme = ColorScheme.fromSeed(
+    seedColor: seedGreen,
+    brightness: Brightness.light,
+  );
+  return ThemeData(
+    useMaterial3: true,
+    colorScheme: scheme,
+    scaffoldBackgroundColor: seedCanvas,
+    appBarTheme: const AppBarTheme(
+      backgroundColor: seedGreen,
+      foregroundColor: Colors.white,
+      elevation: 0,
+      centerTitle: false,
+    ),
+    floatingActionButtonTheme: const FloatingActionButtonThemeData(
+      backgroundColor: seedGreen,
+      foregroundColor: Colors.white,
+    ),
+    bottomSheetTheme: const BottomSheetThemeData(
+      backgroundColor: seedCanvas,
+      surfaceTintColor: Colors.transparent,
+    ),
+    dividerTheme: const DividerThemeData(space: 1, thickness: 1),
+  );
+}