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/GoalPicker.dart

@@ -32,8 +32,8 @@ Future<Goal?> showGoalPicker(
         decoration: const BoxDecoration(
           color: colorSheetBackground,
           borderRadius: BorderRadius.only(
-            topLeft: Radius.circular(28),
-            topRight: Radius.circular(28),
+            topLeft: Radius.zero,
+            topRight: Radius.zero,
           ),
         ),
         child: ListView(
@@ -93,7 +93,7 @@ Widget _goalOption(
       padding: const EdgeInsets.fromLTRB(14, 13, 14, 13),
       decoration: BoxDecoration(
         color: colorWhite,
-        borderRadius: BorderRadius.circular(14),
+        borderRadius: BorderRadius.zero,
         border: Border.all(
           color: selected ? accent.withValues(alpha: 0.5) : colorBorder,
           width: selected ? 1.5 : 1,