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/config.js

@@ -26,7 +26,8 @@ function load() {
       return Object.assign({}, DEFAULTS, JSON.parse(raw));
     }
   } catch (e) {
-    console.error('[config] 读取配置失败，使用默认值:', e.message);
+    const log = require('./logger');
+    log.error('config', '读取配置失败，使用默认值:', e.message);
   }
   return Object.assign({}, DEFAULTS);
 }
@@ -36,7 +37,8 @@ function save(data) {
     fs.mkdirSync(CONFIG_DIR, { recursive: true });
     fs.writeFileSync(CONFIG_FILE, JSON.stringify(data, null, 2), 'utf8');
   } catch (e) {
-    console.error('[config] 写入配置失败:', e.message);
+    const log = require('./logger');
+    log.error('config', '写入配置失败:', e.message);
   }
 }