feat: implement Phase 10 - minimal skeleton with empty grid

Create clean src/ structure with minimal viable implementation:

Core Files:
- src/types.ts: Basic type definitions (Difficulty, GameStatus, GameManager)
- src/index.ts: Main package exports
- src/game.css: Copied from src_old for styling
- src/useGame.ts: Orchestrator with mocked GameManager API
- src/useBoard/useBoard.ts: Renders empty 9x9 sudoku grid

Implementation Details:
- useBoard renders 81 cells with sudoku-grid/sudoku-cell classes
- Each cell has data-r and data-c attributes for identification
- useGame provides full GameManager interface to satisfy example app
- Real implementations: gameStatus, keyLog tracking, game controls
- Mocked implementations: cursor ({}), scoreManager (zeros/null)
- Supports optional platformHook parameter

Build Status:
- TypeScript compiles cleanly with no errors
- Example app builds successfully
- Ready for browser testing with empty grid display

Phase 10 complete. Next: Phase 20 (full useBoard with puzzle generation).

IMPLEMENTATION.md

@@ -63,6 +63,82 @@ vim-sudoku/
 
 ---
 
-## Iteration 2: [Pending]
+## Iteration 2: Phase 10 - Minimal Skeleton
+
+**Date**: 2025-01-22
+
+### Goals
+- Create clean src/ directory structure
+- Implement minimal types
+- Build empty 9x9 grid rendering
+- Mock GameManager API for example app
+- Get visual feedback without errors
+
+### Tasks Completed
+
+#### 1. Created Core Structure
+```
+src/
+├── game.css              [COPIED] - From src_old
+├── index.ts              [CREATED] - Main exports
+├── types.ts              [CREATED] - Basic type definitions
+├── useGame.ts            [CREATED] - Orchestrator with mocks
+└── useBoard/
+    └── useBoard.ts       [CREATED] - Empty grid rendering
+```
+
+#### 2. Implemented Types (src/types.ts)
+- `Difficulty` - Puzzle difficulty levels
+- `GameStatus` - Game state machine states
+- `GameOptions` - useGame configuration
+- `GameManager` - Full API interface (mocked for now)
+- `KeyLogEntry` - Keystroke tracking
+
+#### 3. Implemented useBoard (src/useBoard/useBoard.ts)
+- `containerRef` - DOM reference
+- `renderBoard()` - Renders empty 9x9 sudoku grid
+- Creates proper HTML structure with `sudoku-grid` and `sudoku-cell` classes
+- Sets data attributes (data-r, data-c) for cell identification
+
+#### 4. Implemented useGame (src/useGame.ts)
+- Calls `useBoard()` for grid rendering
+- Returns full `GameManager` interface
+- Real implementations:
+  - `gameStatus` state management
+  - `startGame`, `togglePause`, `quitGame`
+  - `keyLog` tracking with `clearKeyLog`, `getKeyLog`
+- Mocked implementations:
+  - `cursor` (empty object)
+  - `scoreManager` (zeros and null)
+- Supports optional `platformHook` parameter
+
+#### 5. Verified Build
+- ✅ TypeScript compilation successful
+- ✅ Example app builds without errors
+- ✅ No runtime errors expected
+
+### Technical Details
+
+**Empty Grid Rendering**:
+- 81 cells (9x9) created with `sudoku-cell` class
+- Each cell has `data-r` and `data-c` attributes
+- Wrapped in `sudoku-grid` div inside `#sudoku` container
+- Uses CSS from src_old for styling
+
+**Mocking Strategy**:
+- Return full GameManager interface to satisfy example app
+- Mock methods do nothing (empty functions)
+- Mock values return defaults (0, null, empty arrays)
+- Real state management only for critical path (gameStatus)
+
+### Next Steps
+- Phase 20: Implement full useBoard with SudokuGenerator
+  - Port puzzle generation logic
+  - Add board state management
+  - Implement cell validation
+
+---
+
+## Iteration 3: [Pending]
 
 *To be filled as implementation progresses...*