feat: add dynamic ship tracking for sentences mode

- Ship now moves to center of each character as you type
- Calculate and store X position of current character during rendering
- Ship smoothly tracks typing progress across both lines
- Handles line transitions seamlessly
- Creates engaging targeting effect as ship 'shoots' each letter

src/types.ts

@@ -37,6 +37,8 @@ export type FallingLetter = {
   // For line transitions in sentences/paragraphs
   lineTransition?: boolean;
   lineTransitionTime?: number;
+  // For ship tracking in sentences
+  currentCharX?: number; // X position of current character to type
 };
 
 // ============================================================================