Square every corner, enlarge the main surfaces and add a to-do list

Rounded rectangles and round controls are now square across the app; only
status dots, glows, the sun, rings and the breathing circle stay round.
Cards, rows, thumbnails, featured cards, category tiles, the standing card
and the nav are larger. Home gets a quick To-do list kept on the device
(TodoItem in InternalMemory), seeded with sample items in mock mode.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KhQh614DMeYoQEH9SoMRUw

frontend/lib/Grounded/designs/input/CountStepper.dart

@@ -17,7 +17,7 @@ Widget countStepper(
     padding: const EdgeInsets.fromLTRB(14, 10, 8, 10),
     decoration: BoxDecoration(
       color: colorWhite,
-      borderRadius: BorderRadius.circular(12),
+      borderRadius: BorderRadius.zero,
       border: Border.all(color: colorBorder, width: 1),
     ),
     child: Row(
@@ -54,7 +54,7 @@ Widget _stepButton(IconData icon, VoidCallback? onTap) {
       alignment: Alignment.center,
       decoration: BoxDecoration(
         color: enabled ? colorSecondary : colorInset,
-        borderRadius: BorderRadius.circular(10),
+        borderRadius: BorderRadius.zero,
       ),
       child: Icon(icon,
           size: 14, color: enabled ? colorPrimaryDark : colorGrey),