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/CLAUDE.md

@@ -111,7 +111,7 @@ status field. That's what makes honest history and excuse analysis possible.
 
 See `design.md`. In short: sage-to-cream ambient backdrop, frosted glass
 controls, painted `SceneArt` instead of photos, image-led cards, two-tone
-greetings, night pills with a lime spark.
+greetings, square night buttons with a lime spark, no rounded corners.
 
 - Screens are built from `Sheet` (`designs/Shell.dart`); Home, Routines and
   the routine player compose `AmbientBackground` + glass directly.