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>

src/editor.ts

@@ -0,0 +1,93 @@
+import { spawn, spawnSync } from 'node:child_process'
+import { promises as fs } from 'node:fs'
+import path from 'node:path'
+import { videoDir, loadVideoMeta, saveVideoMeta, type VideoTrim } from './store.js'
+
+export class FfmpegUnavailableError extends Error {
+  constructor() {
+    super('ffmpeg 가 설치되어 있지 않습니다. ffmpeg 를 PATH 에 설치한 뒤 다시 시도해 주세요.')
+  }
+}
+
+let resolvedFfmpegPath: string | null = null
+
+export function getFfmpegPath(): string {
+  if (resolvedFfmpegPath) return resolvedFfmpegPath
+  const r = spawnSync('ffmpeg', ['-version'])
+  if (r.status === 0) {
+    resolvedFfmpegPath = 'ffmpeg'
+    return 'ffmpeg'
+  }
+  throw new FfmpegUnavailableError()
+}
+
+/**
+ * 원본 파일을 그대로 둔 채 trim 결과를 edited.<ext> 로 저장한다.
+ * stream copy 를 우선 시도해 빠르게 자르고, 실패하면 재인코딩.
+ */
+export async function applyTrimToVideo(
+  folder: string,
+  videoId: string,
+  trim: VideoTrim
+): Promise<string> {
+  const bin = getFfmpegPath()
+  const meta = await loadVideoMeta(folder, videoId)
+  if (!meta) throw new Error('비디오를 찾을 수 없습니다.')
+  const dir = videoDir(folder, videoId)
+  const inputPath = path.join(dir, meta.originalFile)
+  await fs.access(inputPath)
+
+  const ext = path.extname(meta.originalFile) || '.mp4'
+  const outName = `edited${ext}`
+  const outPath = path.join(dir, outName)
+  const tmpPath = outPath + '.tmp' + ext
+
+  const startSec = Math.max(0, Number(trim.startSec) || 0)
+  const endSec = trim.endSec == null ? null : Math.max(startSec, Number(trim.endSec))
+
+  const baseArgs = ['-y', '-ss', String(startSec)]
+  if (endSec !== null) baseArgs.push('-to', String(endSec))
+  baseArgs.push('-i', inputPath)
+
+  // 시도 1: stream copy (빠름)
+  const copyArgs = [...baseArgs, '-c', 'copy', '-movflags', '+faststart', tmpPath]
+  let ok = await runFfmpeg(bin, copyArgs)
+  if (!ok) {
+    // 시도 2: 재인코딩
+    const encArgs = [
+      ...baseArgs,
+      '-c:v', 'libx264', '-preset', 'veryfast', '-crf', '23',
+      '-c:a', 'aac', '-b:a', '128k',
+      '-movflags', '+faststart',
+      tmpPath
+    ]
+    ok = await runFfmpeg(bin, encArgs)
+    if (!ok) throw new Error('ffmpeg trim 실패')
+  }
+  await fs.rename(tmpPath, outPath)
+
+  meta.editedFile = outName
+  meta.trim = { startSec, endSec }
+  await saveVideoMeta(folder, meta)
+  return outName
+}
+
+function runFfmpeg(bin: string, args: string[]): Promise<boolean> {
+  return new Promise((resolve) => {
+    const child = spawn(bin, args)
+    let stderr = ''
+    child.stderr.on('data', (c) => {
+      stderr = (stderr + c.toString()).slice(-2000)
+    })
+    child.on('error', () => resolve(false))
+    child.on('close', (code) => {
+      if (code === 0) {
+        resolve(true)
+      } else {
+        // 디버그용 stderr 만 콘솔로
+        console.error('[ffmpeg] failed:', stderr.split('\n').slice(-5).join('\n'))
+        resolve(false)
+      }
+    })
+  })
+}