Unlock secret solver via 7 rapid taps on the title

Allows mobile users to access the auto-solver without a keyboard.

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

src/App.css

@@ -33,6 +33,8 @@ body {
   font-weight: 700;
   color: #343a40;
   letter-spacing: -0.5px;
+  user-select: none;
+  -webkit-user-select: none;
 }
 
 .app-main {

src/App.jsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react'
+import React, { useState, useEffect, useRef } from 'react'
 import Board from './components/Board'
 import NumberPad from './components/NumberPad'
 import GameControls from './components/GameControls'
@@ -36,6 +36,19 @@ function App() {
   const [autoSolving, setAutoSolving] = useState(false)
   const [autoBlinkCell, setAutoBlinkCell] = useState(null)
   const [autoCooldown, setAutoCooldown] = useState(false)
+  const titleTapsRef = useRef({ count: 0, lastTap: 0 })
+
+  function handleTitleTap() {
+    if (solveUnlocked) return
+    const now = Date.now()
+    const ref = titleTapsRef.current
+    ref.count = now - ref.lastTap < 800 ? ref.count + 1 : 1
+    ref.lastTap = now
+    if (ref.count >= 7) {
+      setSolveUnlocked(true)
+      ref.count = 0
+    }
+  }
 
   useEffect(() => {
     document.body.style.background = state.darkMode ? '#1a1a2e' : '#f8f9fa'
@@ -124,7 +137,7 @@ function App() {
   return (
     <div className={`app${state.darkMode ? ' dark' : ''}`} style={{ '--hue': hue }}>
       <header className="app-header">
-        <h1>Sudoku</h1>
+        <h1 className="app-title" onClick={handleTitleTap}>Sudoku</h1>
       </header>
 
       <main className="app-main">