feat: implement video site per README spec

- Express + EJS + express-session stack (auth/navbar ported from minecraft_launcher)
- Public: main folder list, folder video grid, internal popup player (/player/:videoId)
- Admin (/op): login, folder CRUD with right-click context menu + add-folder modal
- Admin folder: video grid with right-click edit/rename/delete, "영상 추가" -> editor
- Video editor: drag-drop upload, file picker, YouTube URL probe (ETA + 5분 경고),
  background yt-dlp download with progress polling, navbar title edit, trim controls,
  save runs ffmpeg trim (original preserved)
- Filesystem storage under data/folders/<name>/<videoId>/{meta.json, original.<ext>, edited.<ext>}

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

public/folder.js

@@ -0,0 +1,59 @@
+(function () {
+  var folder = (window.__OP__ || {}).folder
+  var ctxMenu = document.getElementById('ctxMenu')
+  var targetId = null
+  var targetTitle = null
+
+  function showCtx(x, y) {
+    ctxMenu.style.left = x + 'px'
+    ctxMenu.style.top = y + 'px'
+    ctxMenu.hidden = false
+  }
+  function hideCtx() { ctxMenu.hidden = true }
+
+  document.querySelectorAll('.adminVideo').forEach(function (card) {
+    card.addEventListener('contextmenu', function (e) {
+      e.preventDefault()
+      targetId = card.getAttribute('data-id')
+      targetTitle = card.getAttribute('data-title')
+      showCtx(e.clientX, e.clientY)
+    })
+  })
+
+  document.addEventListener('click', function (e) {
+    if (!ctxMenu.contains(e.target)) hideCtx()
+  })
+
+  ctxMenu.addEventListener('click', function (e) {
+    var btn = e.target.closest('button')
+    if (!btn) return
+    var action = btn.getAttribute('data-action')
+    if (action === 'edit') {
+      location.href = '/op/folder/' + encodeURIComponent(folder) + '/video/editor?id=' + encodeURIComponent(targetId)
+    } else if (action === 'rename') {
+      var t = window.prompt('새 영상 제목', targetTitle)
+      if (t && t !== targetTitle) {
+        fetch('/op/folder/' + encodeURIComponent(folder) + '/video/rename', {
+          method: 'POST',
+          headers: { 'content-type': 'application/json' },
+          body: JSON.stringify({ id: targetId, title: t })
+        }).then(function (r) { return r.json() }).then(function (j) {
+          if (j.ok) location.reload()
+          else alert(j.message || '이름 변경 실패')
+        })
+      }
+    } else if (action === 'delete') {
+      if (window.confirm('"' + targetTitle + '" 영상을 정말 삭제할까요?')) {
+        fetch('/op/folder/' + encodeURIComponent(folder) + '/video/delete', {
+          method: 'POST',
+          headers: { 'content-type': 'application/json' },
+          body: JSON.stringify({ id: targetId })
+        }).then(function (r) { return r.json() }).then(function (j) {
+          if (j.ok) location.reload()
+          else alert(j.message || '삭제 실패')
+        })
+      }
+    }
+    hideCtx()
+  })
+})()