feat: bundle yt-dlp and ffmpeg Linux binaries in bin/

Adds precompiled Linux x86_64 binaries for yt-dlp and ffmpeg under bin/.
The processor resolves yt-dlp from bin/ when present, falling back to PATH.
ffmpeg is passed via --ffmpeg-location so yt-dlp uses the bundled binary on o2switch.
BIN_DIR is configurable via env var.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

worker/processor.ts

@@ -1,11 +1,16 @@
 import { spawn } from 'child_process'
-import { readdirSync, statSync } from 'fs'
+import { existsSync, readdirSync, statSync } from 'fs'
 import path from 'path'
 import { prisma } from '@/lib/prisma'
 import { buildYtdlpArgs } from '@/lib/ytdlp'
 import { createToken } from '@/lib/token'
 import { config } from '../config/app.config'
 
+function resolveYtdlpBin(): string {
+  const local = path.join(config.BIN_DIR, 'yt-dlp')
+  return existsSync(local) ? local : 'yt-dlp'
+}
+
 export async function processDownload(downloadId: string): Promise<void> {
   const download = await prisma.download.findUnique({ where: { id: downloadId } })
   if (!download) return
@@ -22,7 +27,7 @@ export async function processDownload(downloadId: string): Promise<void> {
   let stderr = ''
 
   await new Promise<void>((resolve) => {
-    const proc = spawn('yt-dlp', args)
+    const proc = spawn(resolveYtdlpBin(), args)
     proc.stderr.on('data', (chunk: Buffer) => { stderr += chunk.toString() })
 
     proc.on('close', async (code) => {