feat(folders): nested folder tree (max depth 2) + id-based mutations

- new storeDb.ts: DB+FS layer (folders w/ parent_id, videos w/ global id)
- depth cap: sub-folder cannot have children (enforced in createFolder)
- video id: editable anytime (changeVideoId), uniqueness via PK
- routes:
  - public /folder/:topName[/:subName], /video/:topName[/:subName]/:videoId
  - admin /op/folder/:topName[/:subName], id-based /op/folders/:id/*
    and /op/videos/:id/* (rename/changeId/delete/save + idAvailable check)
- views: breadcrumb + subFolder grid; 플레이리스트 추가 button shows at 2단계
- client JS: id-based mutation endpoints, share URL data attribute,
  in-site player pushes share URL to address bar
- store.ts slimmed to Account + readAccounts (FS layer moved to storeDb)
- pickIntId accepts numeric JSON bodies

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

public/dashboard.js

@@ -1,5 +1,6 @@
 (function () {
   var ctxMenu = document.getElementById('ctxMenu')
+  var targetId = null
   var targetName = null
 
   function showCtx(x, y) {
@@ -7,11 +8,12 @@
     ctxMenu.style.top = y + 'px'
     ctxMenu.hidden = false
   }
-  function hideCtx() { ctxMenu.hidden = true; targetName = null }
+  function hideCtx() { ctxMenu.hidden = true; targetId = null; targetName = null }
 
   document.querySelectorAll('.adminFolder').forEach(function (card) {
     card.addEventListener('contextmenu', function (e) {
       e.preventDefault()
+      targetId = card.getAttribute('data-folder-id')
       targetName = card.getAttribute('data-name')
       showCtx(e.clientX, e.clientY)
     })
@@ -23,15 +25,15 @@
 
   ctxMenu.addEventListener('click', function (e) {
     var btn = e.target.closest('button')
-    if (!btn) return
+    if (!btn || !targetId) return
     var action = btn.getAttribute('data-action')
     if (action === 'rename') {
       var newName = window.prompt('새 폴더 이름', targetName)
       if (newName && newName !== targetName) {
-        fetch('/op/folders/rename', {
+        fetch('/op/folders/' + encodeURIComponent(targetId) + '/rename', {
           method: 'POST',
           headers: { 'content-type': 'application/json' },
-          body: JSON.stringify({ oldName: targetName, newName: newName })
+          body: JSON.stringify({ newName: newName })
         }).then(function (r) { return r.json() }).then(function (j) {
           if (j.ok) location.reload()
           else alert(j.message || '이름 변경 실패')
@@ -39,10 +41,8 @@
       }
     } else if (action === 'delete') {
       if (window.confirm('"' + targetName + '" 폴더를 정말 삭제할까요? 안의 영상이 모두 사라집니다.')) {
-        fetch('/op/folders/delete', {
-          method: 'POST',
-          headers: { 'content-type': 'application/json' },
-          body: JSON.stringify({ name: targetName })
+        fetch('/op/folders/' + encodeURIComponent(targetId) + '/delete', {
+          method: 'POST'
         }).then(function (r) { return r.json() }).then(function (j) {
           if (j.ok) location.reload()
           else alert(j.message || '삭제 실패')
@@ -61,20 +61,22 @@
 
   function openModal() { modal.hidden = false; input.value = ''; setTimeout(function () { input.focus() }, 0) }
   function closeModal() { modal.hidden = true }
-  addBtn.addEventListener('click', openModal)
-  cancelBtn.addEventListener('click', closeModal)
-  modal.addEventListener('click', function (e) { if (e.target === modal) closeModal() })
-  input.addEventListener('keydown', function (e) { if (e.key === 'Enter') confirmBtn.click() })
-  confirmBtn.addEventListener('click', function () {
-    var name = input.value.trim()
-    if (!name) return
-    fetch('/op/folders', {
-      method: 'POST',
-      headers: { 'content-type': 'application/json' },
-      body: JSON.stringify({ name: name })
-    }).then(function (r) { return r.json() }).then(function (j) {
-      if (j.ok) location.reload()
-      else alert(j.message || '폴더 생성 실패')
+  if (addBtn) {
+    addBtn.addEventListener('click', openModal)
+    cancelBtn.addEventListener('click', closeModal)
+    modal.addEventListener('click', function (e) { if (e.target === modal) closeModal() })
+    input.addEventListener('keydown', function (e) { if (e.key === 'Enter') confirmBtn.click() })
+    confirmBtn.addEventListener('click', function () {
+      var name = input.value.trim()
+      if (!name) return
+      fetch('/op/folders', {
+        method: 'POST',
+        headers: { 'content-type': 'application/json' },
+        body: JSON.stringify({ name: name })
+      }).then(function (r) { return r.json() }).then(function (j) {
+        if (j.ok) location.reload()
+        else alert(j.message || '폴더 생성 실패')
+      })
     })
-  })
+  }
 })()