fix: clean up empty catch blocks in backend utilities

修复了后端工具文件中的 10 个空 catch 块：
- system-crypto.ts: 修复 1 个空 catch 块
- server-stats.ts: 修复 4 个空 catch 块
- auto-ssl-setup.ts: 修复 1 个空 catch 块
- ssh-key-utils.ts: 修复 4 个空 catch 块

所有空块都添加了描述性注释说明为何忽略错误。

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

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

src/backend/utils/auto-ssl-setup.ts

@@ -234,7 +234,9 @@ IP.3 = 0.0.0.0
     let envContent = "";
     try {
       envContent = await fs.readFile(this.ENV_FILE, "utf8");
-    } catch {}
+    } catch {
+      // File doesn't exist yet, will create with SSL config
+    }
 
     let updatedContent = envContent;
     let hasChanges = false;

src/backend/utils/ssh-key-utils.ts

@@ -84,7 +84,9 @@ function detectKeyTypeFromContent(keyContent: string): string {
       } else if (decodedString.includes("1.3.101.112")) {
         return "ssh-ed25519";
       }
-    } catch (error) {}
+    } catch {
+      // Cannot decode key, fallback to length-based detection
+    }
 
     if (content.length < 800) {
       return "ssh-ed25519";
@@ -140,7 +142,9 @@ function detectPublicKeyTypeFromContent(publicKeyContent: string): string {
       } else if (decodedString.includes("1.3.101.112")) {
         return "ssh-ed25519";
       }
-    } catch (error) {}
+    } catch {
+      // Cannot decode key, fallback to length-based detection
+    }
 
     if (content.length < 400) {
       return "ssh-ed25519";
@@ -242,7 +246,9 @@ export function parseSSHKey(
 
           useSSH2 = true;
         }
-      } catch (error) {}
+      } catch {
+        // SSH2 parsing failed, will use fallback method
+      }
     }
 
     if (!useSSH2) {
@@ -268,7 +274,9 @@ export function parseSSHKey(
           success: true,
         };
       }
-    } catch (fallbackError) {}
+    } catch {
+      // Fallback parsing also failed
+    }
 
     return {
       privateKey: privateKeyData,

src/backend/utils/system-crypto.ts

@@ -115,7 +115,9 @@ class SystemCrypto {
           process.env.INTERNAL_AUTH_TOKEN = tokenMatch[1];
           return;
         }
-      } catch {}
+      } catch {
+        // Ignore file read errors, will generate new token
+      }
 
       await this.generateAndGuideInternalAuthToken();
     } catch (error) {