feat: prepare vim-sudoku for unified API implementation

- Archive previous implementation attempt (src -> src_failed)
- Create comprehensive IMPLEMENTATION_PLAN.md with phased approach
- Create IMPLEMENTATION.md to track implementation progress
- Update example app to match vim-maze patterns:
  - Simplify UI to desktop-only (no mobile support)
  - Add score metrics display (time, keystrokes, final score)
  - Update instructions for sudoku-specific keys (hjkl, i for edit)
  - Remove unnecessary mobile hooks

Phase 5 complete. Ready to begin Phase 10 (Setup & Core Types).

IMPLEMENTATION.md

@@ -0,0 +1,68 @@
+# vim-sudoku Unified API Implementation Log
+
+This document tracks the step-by-step implementation of the unified API architecture for vim-sudoku.
+
+## Overview
+
+We are porting vim-sudoku from the old architecture (src_old) to follow the unified API patterns established by vim-maze. This enables consistent architecture across all VIMazing games and better platform integration.
+
+---
+
+## Iteration 1: Preparation & Planning
+
+**Date**: 2025-01-22
+
+### Goals
+- Review existing implementations (vim-maze, src_old, src_failed)
+- Create implementation plan
+- Prepare example app for new API
+
+### Tasks Completed
+
+#### 1. Reviewed Architecture
+- Analyzed vim-maze unified API implementation
+- Examined src_old working implementation
+- Identified src_failed attempt issues
+- Documented key differences between vim-maze and vim-sudoku
+
+#### 2. Created Implementation Plan
+- Created `IMPLEMENTATION_PLAN.md` with 7 phases (numbered x10 for flexibility)
+- Defined file structure matching vim-maze patterns
+- Documented key design decisions
+- Established type mappings between vim-maze and vim-sudoku
+- Listed success criteria
+
+#### 3. Prepared Example App (Phase 5)
+- Updated `example/src/App.tsx` to match vim-maze structure
+- Simplified to desktop-only (no mobile support)
+- Added score metrics display (time, keystrokes, final score)
+- Updated game status messages for sudoku context
+- Changed navigation instructions (hjkl + i for edit mode)
+- Verified `useKeyBindings` already matches vim-maze
+
+### File Changes
+```
+vim-sudoku/
+├── IMPLEMENTATION_PLAN.md       [CREATED] - Detailed implementation roadmap
+├── IMPLEMENTATION.md             [CREATED] - This file, tracking progress
+├── example/src/App.tsx           [MODIFIED] - Simplified, sudoku-focused UI
+└── src/ → src_failed/            [RENAMED] - Previous failed attempt archived
+```
+
+### Key Decisions
+
+1. **No Mobile Support**: Sudoku with vim bindings requires keyboard, mobile not practical
+2. **Simple Metrics**: Start with time, keystrokes, and final score (no efficiency yet)
+3. **Phase Numbering**: Use x10 numbering (10, 20, 30...) to allow insertions
+
+### Next Steps
+- Phase 10: Setup & Core Types
+  - Create clean src/ directory structure
+  - Define all type definitions
+  - Set up module exports
+
+---
+
+## Iteration 2: [Pending]
+
+*To be filled as implementation progresses...*