feat: add structured logging, process watchdog, and systemd hardening

- Add lib/logger.js: timestamped structured logging with 5MB x 5 file rotation
- Add lib/watchdog.js: generic child process supervisor with rate-limited restarts
- Enhance client.js: WS ping/pong liveness detection, uncaughtException/unhandledRejection handlers, systemd sd-notify integration
- Refactor frpc.js: FrpcManager now delegates to Watchdog instead of manual spawn/exit
- Enhance install.sh: environment file, log directory, systemd resource limits, security hardening, WatchdogSec=60
- Replace all console.log/warn/error with structured logger across modules

Made-with: Cursor

lib/fingerprint.js

@@ -104,7 +104,8 @@ function getPersistentUUID() {
     fs.writeFileSync(PERSIST_FILE, id, 'utf8');
   } catch (e) {
     // 写不进去也没关系，本次用内存值（重启后会变，但这是最后兜底）
-    console.warn('[fingerprint] 无法持久化 box_id:', e.message);
+    const log = require('./logger');
+    log.warn('fingerprint', '无法持久化 box_id:', e.message);
   }
   return id;
 }