Implement Phase 10: e-ink polish and finalize project docs

- High-contrast theme with expanded color palette for e-ink readability
- Updated source trees in DESIGN.md
- Updated PROJECT_PLAN.md and PROGRESS.md — all phases complete
  (only on-device performance profiling remains)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

DESIGN.md

@@ -305,7 +305,9 @@ eng-pad/
 │       │   │   │       └── Theme.kt                  -- Material3 theme
 │       │   │   └── undo/
 │       │   │       ├── UndoManager.kt                -- Undo/redo stack
-│       │   │       └── UndoableAction.kt             -- Action interface + impls
+│       │   │       ├── UndoableAction.kt             -- Action interface
+│       │   │       ├── StrokeActions.kt              -- Add/delete stroke actions
+│       │   │       └── SelectionActions.kt           -- Multi-stroke delete/move/copy
 │       │   └── res/
 │       │       ├── values/
 │       │       │   ├── strings.xml