fix: integrate hint buttons into table for perfect row alignment and sticky scroll

Move hint buttons from a separate flex column into the table as the
first <td> of each row, ensuring pixel-perfect alignment with grid rows.
Use position:sticky with box-shadow to keep hints fixed on the left
while scrolling horizontally.

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

assets/react/controllers/GameRow.jsx

@@ -1,11 +1,12 @@
 import React, { useRef, useCallback, useMemo } from 'react';
 import LetterInput from './LetterInput';
+import ActorPopover from './ActorPopover';
 
 function isLetter(ch) {
     return /[a-zA-Z]/.test(ch);
 }
 
-export default function GameRow({ actorName, pos, colStart, totalWidth }) {
+export default function GameRow({ actorName, pos, colStart, totalWidth, hintType, hintText }) {
     const inputRefs = useRef([]);
     const letters = actorName.split('');
 
@@ -28,6 +29,9 @@ export default function GameRow({ actorName, pos, colStart, totalWidth }) {
 
     return (
         <tr>
+            <td className="hint-cell">
+                <ActorPopover hintType={hintType} hintText={hintText} />
+            </td>
             {Array.from({ length: totalWidth + 1 }, (_, colIndex) => {
                 const charIndex = colIndex - colStart;
                 const isInRange = charIndex >= 0 && charIndex < letters.length;