Switch to PM2, add deploy script

- Replace tmux with PM2 process manager
- Add deploy script (pnpm deploy = build + pm2 reload)
- PM2 auto-starts on boot via systemd (pm2-root.service)
- Remove old atom-nexst.service (direct next start)

package.json

@@ -11,6 +11,7 @@
 		"build": "next build",
 		"postbuild": "mkdir -p .next/standalone/.next/static && cp -r .next/static/* .next/standalone/.next/static/ 2>/dev/null; true",
 		"start": "node .next/standalone/server.js",
+		"deploy": "pnpm build && pm2 reload next --update-env",
 		"prisma:generate": "prisma generate",
 		"typecheck": "tsc --noEmit --incremental false",
 		"biome:check": "biome check --write .",