Add secret auto-solver unlocked via Konami code

Logical-only solver (naked + hidden singles, no backtracking) fills one
cell every ~2-3s with a blink animation, so progress is only made when
the deduction is certain.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/Board.jsx

@@ -2,7 +2,7 @@ import React from 'react'
 import Cell from './Cell'
 import { checkValue } from '../utils/sudoku'
 
-function Board({ board, puzzle, solution, notes, selected, highlightedNumber, showErrors, celebrating, selectCell, deselect }) {
+function Board({ board, puzzle, solution, notes, selected, highlightedNumber, showErrors, celebrating, autoBlinkCell, selectCell, deselect }) {
   const selectedValue = selected && board[selected.row][selected.col]
   const activeNumber = selected ? selectedValue : highlightedNumber
 
@@ -31,6 +31,8 @@ function Board({ board, puzzle, solution, notes, selected, highlightedNumber, sh
             value !== 0 &&
             !checkValue(solution, r, c, value)
           const isCelebrating = celebrating.has(`${r},${c}`)
+          const isAutoBlinking =
+            autoBlinkCell && autoBlinkCell.row === r && autoBlinkCell.col === c
 
           return (
             <Cell
@@ -45,6 +47,7 @@ function Board({ board, puzzle, solution, notes, selected, highlightedNumber, sh
               isSameNumber={isSameNumber}
               isError={isError}
               isCelebrating={isCelebrating}
+              isAutoBlinking={isAutoBlinking}
               onClick={(e) => e.ctrlKey || e.metaKey ? deselect() : selectCell(r, c)}
             />
           )

src/components/Cell.jsx

@@ -1,6 +1,6 @@
 import React from 'react'
 
-function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlightedCol, isHighlightedBox, isSameNumber, isError, isCelebrating, onClick }) {
+function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlightedCol, isHighlightedBox, isSameNumber, isError, isCelebrating, isAutoBlinking, onClick }) {
   const classes = ['cell']
   if (isGiven) classes.push('given')
   if (isSelected) classes.push('selected')
@@ -10,6 +10,7 @@ function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlight
   if (isSameNumber) classes.push('same-number')
   if (isError) classes.push('error')
   if (isCelebrating) classes.push('celebrating')
+  if (isAutoBlinking) classes.push('auto-blinking')
 
   return (
     <div className={classes.join(' ')} onClick={onClick}>

src/components/GameControls.jsx

@@ -8,7 +8,7 @@ const DIFFICULTIES = [
   { value: 'expert', label: 'Expert' },
 ]
 
-function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, canUndo, canRedo, onOpenSettings }) {
+function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, canUndo, canRedo, onOpenSettings, solveUnlocked, autoSolving, onToggleAutoSolve }) {
   const [difficulty, setDifficulty] = useState(currentDifficulty)
   const [showConfirm, setShowConfirm] = useState(false)
 
@@ -32,6 +32,11 @@ function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, c
         <button className="btn btn-primary" onClick={() => setShowConfirm(true)}>
           Nova Partida
         </button>
+        {solveUnlocked && (
+          <button className="btn btn-secondary" onClick={onToggleAutoSolve}>
+            {autoSolving ? 'Atura' : 'Resol'}
+          </button>
+        )}
       </div>
       <div className="controls-row">
         <button className="btn btn-secondary" onClick={onClear} title="Esborra">