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/buttons/Buttons.dart

@@ -27,7 +27,7 @@ Widget roundedCornerButton(
       disabledBackgroundColor: colorGrey.withValues(alpha: 0.4),
       padding: EdgeInsets.symmetric(vertical: verticalPadding),
       shape: RoundedRectangleBorder(
-        borderRadius: BorderRadius.circular(radius),
+        borderRadius: BorderRadius.zero,
       ),
     ),
     child: Row(
@@ -65,7 +65,7 @@ Widget outlinedActionButton(
       side: BorderSide(color: fg.withValues(alpha: 0.35), width: 1),
       padding: const EdgeInsets.symmetric(vertical: 16),
       shape: RoundedRectangleBorder(
-        borderRadius: BorderRadius.circular(radius),
+        borderRadius: BorderRadius.zero,
       ),
     ),
     child: Row(
@@ -112,7 +112,7 @@ Widget iconButton(
       alignment: Alignment.center,
       decoration: BoxDecoration(
         color: background ?? Colors.transparent,
-        borderRadius: BorderRadius.circular(radius),
+        borderRadius: BorderRadius.zero,
         border: bordered
             ? Border.all(color: borderColor ?? colorBorder, width: 1)
             : null,
@@ -161,7 +161,7 @@ Widget segmentedSelector<T>({
           padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 10),
           decoration: BoxDecoration(
             color: isSelected ? active : colorWhite,
-            borderRadius: BorderRadius.circular(10),
+            borderRadius: BorderRadius.zero,
             border: Border.all(
               color: isSelected ? active : colorBorder,
               width: 1,