Step 4: replace stacked sub-steps with single-slot wizard flow

- renderStep4 now renders 4-1/4-2/4-3 into one #subHost slot, replacing instead of stacking when 다음 is clicked
- 4-2 shows "다음" only after install completes so success message stays visible (previously auto-advanced and the message flashed)
- Drop the duplicate section-level "5단계로" button; 4-3's confirm button advances to step 5

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

installer/renderer.js

@@ -402,29 +402,30 @@ function renderStep4() {
   section.className = 'page'
   section.innerHTML =
     '<h2>4단계. 유저 클라이언트 설정</h2>' +
-    '<div class="subStep" id="sub41"></div>' +
-    '<div class="subStep" id="sub42" hidden></div>' +
-    '<div class="subStep" id="sub43" hidden></div>' +
-    '<div class="actionRow"><button class="secondaryBtn" id="back">이전</button><button class="primaryBtn" id="next" hidden>5단계로</button></div>'
+    '<div class="subStep" id="subHost"></div>' +
+    '<div class="actionRow"><button class="secondaryBtn" id="back">이전</button><span></span></div>'
   pageHost.appendChild(section)
+  var subHost = section.querySelector('#subHost')
   section.querySelector('#back').addEventListener('click', function () {
     if (state.mode === 'multi') renderStep3(); else renderStep2()
   })
 
-  renderSubStep41(section.querySelector('#sub41'), pack, function () {
-    section.querySelector('#sub42').hidden = false
-    renderSubStep42(section.querySelector('#sub42'), function () {
-      section.querySelector('#sub43').hidden = false
-      renderSubStep43(section.querySelector('#sub43'), function () {
-        var nextBtn = section.querySelector('#next')
-        nextBtn.hidden = false
-        nextBtn.addEventListener('click', function () {
-          state.stepDone[4] = true
-          renderStep5()
-        })
-      })
+  function show41() {
+    subHost.innerHTML = ''
+    renderSubStep41(subHost, pack, show42)
+  }
+  function show42() {
+    subHost.innerHTML = ''
+    renderSubStep42(subHost, show43)
+  }
+  function show43() {
+    subHost.innerHTML = ''
+    renderSubStep43(subHost, function () {
+      state.stepDone[4] = true
+      renderStep5()
     })
-  })
+  }
+  show41()
 }
 
 function renderSubStep41(host, pack, done) {
@@ -479,9 +480,13 @@ function renderSubStep42(host, done) {
     '<h3>4-2. 모드/리소스팩 다운로드 및 launcher_profiles 갱신</h3>' +
     '<p class="formMessage">%appdata%\\.mc_custom 에 모드와 리소스팩을 설치하고, launcher_profiles.json에 프로필을 등록합니다.</p>' +
     '<button class="primaryBtn" id="run">설치 시작</button>' +
-    '<div class="formMessage" id="msg"></div>'
-  host.querySelector('#run').addEventListener('click', async function () {
-    var msg = host.querySelector('#msg')
+    '<div class="formMessage" id="msg"></div>' +
+    '<div class="actionRow"><span></span><button class="primaryBtn" id="next" hidden>다음</button></div>'
+  var runBtn = host.querySelector('#run')
+  var msg = host.querySelector('#msg')
+  var nextBtn = host.querySelector('#next')
+  runBtn.addEventListener('click', async function () {
+    runBtn.disabled = true
     msg.textContent = '설치 중...'
     msg.classList.remove('error', 'success')
     try {
@@ -491,12 +496,14 @@ function renderSubStep42(host, done) {
       })
       msg.textContent = '클라이언트 설치 완료.'
       msg.classList.add('success')
-      done()
+      nextBtn.hidden = false
     } catch (err) {
       msg.textContent = '설치 실패: ' + err.message
       msg.classList.add('error')
+      runBtn.disabled = false
     }
   })
+  nextBtn.addEventListener('click', done)
 }
 
 function renderSubStep43(host, done) {