feat(ui): Material 3 redesign, cover-photo viewer, About screen

Apply a Material 3 seed-green palette and rounded components across the
home, inventory, quick-add, quantity picker and variety-detail screens.
The full-screen photo viewer can now set any photo as the cover (via
attachment sort order) and delete after confirmation. Lot forms and
packaging surface as choice chips.

Extract About out of Settings into its own screen (app version via
package_info_plus, website link). Add es/en strings for the new lot
types, presentation, home tagline and About. Update Seedees v2 mockups.

apps/app_seeds/lib/ui/theme.dart

@@ -1,35 +1,104 @@
 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);
+/// Material 3 palette from the Seedees v2 redesign
+/// (docs/mockups/seedees_material3.html): green app bars over a pale-green
+/// canvas, a saturated green for primary actions (FAB, buttons, links, category
+/// headers) and a soft green container for selected/tonal surfaces.
+const seedGreen = Color(0xFF2F7D34); // primary (actions, links, headers)
+const seedGreenDark = Color(0xFF22521E); // status bar / darker green
+const seedAppBar = Color(0xFF3E8C38); // app-bar green
+const seedCanvas = Color(0xFFE7F1E0); // surface / scaffold
+const seedPrimaryContainer = Color(0xFFD3E8C8); // tonal green container
+const seedOnPrimaryContainer = Color(0xFF2F6D2A);
+const seedField = Color(0xFFF3F7EE); // outlined field fill
+const seedAvatar = Color(0xFFCFE7C3); // list avatar disc
+const seedOnAvatar = Color(0xFF3B7A34);
+const seedOutline = Color(0xFFC3CBB6);
+const seedDivider = Color(0xFFE4E9DD);
+const seedTitle = Color(0xFF1B2416); // heading text on canvas
+const seedOnSurface = Color(0xFF1B2416);
+const seedOnSurfaceVariant = Color(0xFF5C6B52); // scientific names, secondary
+const seedMuted = Color(0xFF8A9880); // hints, list edit icon
+const seedRating = Color(0xFFE8A200); // stars
 
 ThemeData buildTaneTheme() {
-  final scheme = ColorScheme.fromSeed(
-    seedColor: seedGreen,
-    brightness: Brightness.light,
-  );
+  final scheme =
+      ColorScheme.fromSeed(
+        seedColor: seedGreen,
+        brightness: Brightness.light,
+      ).copyWith(
+        primary: seedGreen,
+        onPrimary: Colors.white,
+        primaryContainer: seedPrimaryContainer,
+        onPrimaryContainer: seedOnPrimaryContainer,
+        secondaryContainer: seedPrimaryContainer,
+        onSecondaryContainer: seedOnPrimaryContainer,
+        tertiary: seedRating,
+        onTertiary: Colors.white,
+        surface: seedCanvas,
+        onSurface: seedOnSurface,
+        surfaceContainerHighest: seedField,
+        onSurfaceVariant: seedOnSurfaceVariant,
+        outline: seedMuted,
+        outlineVariant: seedOutline,
+      );
   return ThemeData(
     useMaterial3: true,
     colorScheme: scheme,
     scaffoldBackgroundColor: seedCanvas,
+    // Green app bars — aligned with the v2 mockups and the real app.
     appBarTheme: const AppBarTheme(
-      backgroundColor: seedGreen,
+      backgroundColor: seedAppBar,
       foregroundColor: Colors.white,
+      surfaceTintColor: Colors.transparent,
       elevation: 0,
+      scrolledUnderElevation: 0,
       centerTitle: false,
+      iconTheme: IconThemeData(color: Colors.white),
+      titleTextStyle: TextStyle(
+        color: Colors.white,
+        fontSize: 20,
+        fontWeight: FontWeight.w500,
+      ),
     ),
-    floatingActionButtonTheme: const FloatingActionButtonThemeData(
+    // Squircle FAB (20px radius) as in the mockups, in the saturated primary.
+    floatingActionButtonTheme: FloatingActionButtonThemeData(
       backgroundColor: seedGreen,
       foregroundColor: Colors.white,
+      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(20)),
+    ),
+    drawerTheme: const DrawerThemeData(
+      backgroundColor: Colors.white,
+      surfaceTintColor: Colors.transparent,
     ),
     bottomSheetTheme: const BottomSheetThemeData(
       backgroundColor: seedCanvas,
       surfaceTintColor: Colors.transparent,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.vertical(top: Radius.circular(26)),
+      ),
+    ),
+    // Pill "Save" actions across sheets and dialogs, as in the v3 mockups.
+    filledButtonTheme: FilledButtonThemeData(
+      style: FilledButton.styleFrom(
+        backgroundColor: seedGreen,
+        foregroundColor: Colors.white,
+        shape: const StadiumBorder(),
+        padding: const EdgeInsets.symmetric(horizontal: 28, vertical: 13),
+      ),
+    ),
+    textButtonTheme: TextButtonThemeData(
+      style: TextButton.styleFrom(foregroundColor: seedGreen),
+    ),
+    // Green floating labels on the edit-seed / add-batch text fields. (Borders
+    // are left to each field so the inventory search keeps its borderless pill.)
+    inputDecorationTheme: const InputDecorationTheme(
+      floatingLabelStyle: TextStyle(color: seedGreen),
+    ),
+    dividerTheme: const DividerThemeData(
+      space: 1,
+      thickness: 1,
+      color: seedDivider,
     ),
-    dividerTheme: const DividerThemeData(space: 1, thickness: 1),
   );
 }