feat: implement game modes system with letters and words support

- Add GameMode type: 'letters' | 'words' | 'sentences' | 'paragraphs'
- Add gameMode option to GameOptions (defaults to 'letters')
- Create wordLists.ts with curated word lists for each mode
- Update FallingLetter type to track:
  - fullText: complete word/sentence/paragraph
  - charIndex: current character progress in word
- Modify word spawning to pick from mode-specific word list
- Update handleTypedLetter to support multi-character typed sequences:
  - Track progress through word (charIndex)
  - Advance to next character when correct
  - Show complete word only when fully typed
- Enhanced canvas rendering with color-coded progress:
  - Green: completed characters
  - Yellow: current character being typed
  - White: remaining characters
- Add mode selector buttons to example app
- Default to 'words' mode in example for testing
- Full TypeScript support for all modes

src/types.ts

@@ -7,6 +7,7 @@ import type { RefObject } from 'react';
 export type GameStatus = 'waiting' | 'started' | 'game-won' | 'game-over';
 export type GamePhase = 'idle' | 'playing';
 export type PlayStatus = 'started' | 'game-over' | 'game-won';
+export type GameMode = 'letters' | 'words' | 'sentences' | 'paragraphs';
 
 export const isPlaying = (status: GameStatus): status is PlayStatus =>
   status === 'started' || status === 'game-over' || status === 'game-won';
@@ -30,6 +31,9 @@ export type FallingLetter = {
   y: number; // 0-600 pixel position
   state: LetterState;
   stateStartTime?: number; // For animation timing
+  // For word/sentence/paragraph modes
+  fullText?: string; // The complete word/sentence/paragraph
+  charIndex?: number; // Current character index being typed (0-based)
 };
 
 // ============================================================================
@@ -39,7 +43,7 @@ export type FallingLetter = {
 export type KeyLogEntry = { key: string; timestamp: number };
 
 export type GameOptions = {
-  // TODO: Define game options
+  gameMode?: GameMode;
 };
 
 // ============================================================================