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/app.ts

@@ -0,0 +1,70 @@
+import express from 'express'
+import session from 'express-session'
+import path from 'node:path'
+import fsp from 'node:fs/promises'
+import { dataDir, foldersDir, jobsDir, tmpDir, publicDir, viewsDir } from './paths.js'
+import { publicRouter } from './routes/public.js'
+import { opRouter } from './routes/op.js'
+
+async function ensureDirs(): Promise<void> {
+  for (const dir of [dataDir, foldersDir, jobsDir, tmpDir]) {
+    await fsp.mkdir(dir, { recursive: true })
+  }
+}
+
+async function main(): Promise<void> {
+  await ensureDirs()
+
+  const PORT = Number(process.env.PORT ?? 3000)
+  const HOST = process.env.HOST ?? '127.0.0.1'
+
+  const app = express()
+  app.set('view engine', 'ejs')
+  app.set('views', viewsDir)
+  app.set('trust proxy', 1)
+
+  app.use(express.urlencoded({ extended: true }))
+  app.use(express.json({ limit: '4mb' }))
+
+  app.use(session({
+    secret: process.env.SESSION_SECRET ?? 'make-video-site-dev-secret',
+    resave: false,
+    saveUninitialized: false,
+    cookie: {
+      httpOnly: true,
+      sameSite: 'lax',
+      maxAge: 1000 * 60 * 60 * 8
+    }
+  }))
+
+  // account.json 직접 노출 차단
+  app.use((req, res, next) => {
+    if (/^\/account\.json/i.test(req.path)) {
+      res.status(404).send('Not Found')
+      return
+    }
+    next()
+  })
+
+  app.use('/static', express.static(publicDir))
+
+  app.use('/', publicRouter)
+  app.use('/', opRouter)
+
+  app.use((err: unknown, _req: express.Request, res: express.Response, _next: express.NextFunction) => {
+    console.error(err)
+    const message = err instanceof Error ? err.message : '알 수 없는 오류'
+    if (res.headersSent) return
+    res.status(500).send(`서버 오류: ${message}`)
+  })
+
+  app.listen(PORT, HOST, () => {
+    console.log(`[server] http://${HOST}:${PORT}`)
+    console.log(`[server] views: ${path.relative(process.cwd(), viewsDir)}`)
+  })
+}
+
+main().catch((err) => {
+  console.error(err)
+  process.exit(1)
+})