fix: clean up empty catch blocks in frontend components

修复了前端组件中的空 catch 块：
- Tunnel.tsx: 修复空 catch 块并添加注释
- ServerConfig.tsx: 修复空 catch 块并添加注释
- TerminalKeyboard.tsx: 修复空 catch 块并添加注释
- system-crypto.ts: 修复遗漏的空 catch 块

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/backend/utils/system-crypto.ts

@@ -76,7 +76,9 @@ class SystemCrypto {
           process.env.DATABASE_KEY = dbKeyMatch[1];
           return;
         }
-      } catch {}
+      } catch {
+        // Ignore file read errors, will generate new key
+      }
 
       await this.generateAndGuideDatabaseKey();
     } catch (error) {