feat(installer): 최종 리소스팩 다운로드 진행률(퍼센트) 표시

"예" 선택 후 최종 리소스팩 다운로드 시 퍼센트/진행바를 보여준다.
- finalResourcepack:install 을 downloadFile → downloadStream 으로 바꿔 content-length
  기반 진행률을 계산하고 finalResourcepack:progress 이벤트로 렌더러에 전송.
- preload onFinalResourcepackProgress 구독 추가, 렌더러에 진행바+% 표시(완료 100%,
  실패 시 바 숨김). 0.4.17→0.4.18.

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

installer/renderer.js

@@ -1133,20 +1133,47 @@ function downloadFinalResourcepack() {
   section.innerHTML =
     '<h2>' + tt('resourcepack.downloadHeading') + '</h2>' +
     '<div class="formMessage" id="rpMsg">' + tt('resourcepack.downloading') + '</div>' +
+    '<div id="rpBarWrap" style="margin-top:10px;height:16px;background:rgba(255,255,255,0.08);border:1px solid var(--border,#30363d);border-radius:8px;overflow:hidden;">' +
+    '  <div id="rpBar" style="height:100%;width:0%;background:var(--accent,#6cf);transition:width 0.15s;"></div>' +
+    '</div>' +
+    '<div class="formMessage" id="rpPercent" style="margin-top:6px;">0%</div>' +
     '<div class="actionRow" id="rpActions" hidden></div>'
   pageHost.appendChild(section)
   var msg = section.querySelector('#rpMsg')
   var actions = section.querySelector('#rpActions')
+  var bar = section.querySelector('#rpBar')
+  var barWrap = section.querySelector('#rpBarWrap')
+  var percentEl = section.querySelector('#rpPercent')
 
-  function proceed() { state.finalRpHandled = true; renderStep5() }
+  // 다운로드 진행률(퍼센트) 구독. 완료/실패 시 해제.
+  var unsubscribe = null
+  if (installerApi.onFinalResourcepackProgress) {
+    unsubscribe = installerApi.onFinalResourcepackProgress(function (info) {
+      if (info && info.percent >= 0) {
+        bar.style.width = info.percent + '%'
+        percentEl.textContent = info.percent + '%'
+      } else if (info) {
+        // 전체 크기를 모르면 받은 용량(MB)만 표시.
+        percentEl.textContent = (info.loaded / 1048576).toFixed(1) + ' MB'
+      }
+    })
+  }
+  function stopProgress() { if (unsubscribe) { unsubscribe(); unsubscribe = null } }
+
+  function proceed() { stopProgress(); state.finalRpHandled = true; renderStep5() }
 
   installerApi.installFinalResourcepack().then(function (res) {
+    stopProgress()
     if (res && res.ok) {
+      bar.style.width = '100%'
+      percentEl.textContent = '100%'
       msg.textContent = tt('resourcepack.downloadDone')
       msg.classList.add('success')
       actions.innerHTML = '<button class="primaryBtn" id="rpNext">' + tt('common.next') + '</button>'
       actions.querySelector('#rpNext').addEventListener('click', proceed)
     } else {
+      barWrap.hidden = true
+      percentEl.hidden = true
       msg.textContent = tt('resourcepack.downloadFailed', { message: (res && res.message) || 'unknown' })
       msg.classList.add('error')
       actions.innerHTML =
@@ -1157,6 +1184,9 @@ function downloadFinalResourcepack() {
     }
     actions.hidden = false
   }).catch(function (err) {
+    stopProgress()
+    barWrap.hidden = true
+    percentEl.hidden = true
     msg.textContent = tt('resourcepack.downloadFailed', { message: (err && err.message) ? err.message : String(err) })
     msg.classList.add('error')
     actions.innerHTML =