fix(typescript): tighten TypeScript null safety and error handling across backend and ops UI

ts/security/classes.contentscanner.ts

@@ -60,7 +60,7 @@ export enum ThreatCategory {
  * Content Scanner for detecting malicious email content
  */
 export class ContentScanner {
-  private static instance: ContentScanner;
+  private static instance: ContentScanner | undefined;
   private scanCache: LRUCache<string, IScanResult>;
   private options: Required<IContentScannerOptions>;
   
@@ -258,12 +258,12 @@ export class ContentScanner {
       }
       
       return result;
-    } catch (error) {
-      logger.log('error', `Error scanning email: ${error.message}`, {
+    } catch (error: unknown) {
+      logger.log('error', `Error scanning email: ${(error as Error).message}`, {
         messageId: email.getMessageId(),
-        error: error.stack
+        error: (error as Error).stack
       });
-      
+
       // Return a safe default with error indication
       return {
         isClean: true, // Let it pass if scanner fails (configure as desired)
@@ -271,7 +271,7 @@ export class ContentScanner {
         scannedElements: ['error'],
         timestamp: Date.now(),
         threatType: 'scan_error',
-        threatDetails: `Scan error: ${error.message}`
+        threatDetails: `Scan error: ${(error as Error).message}`
       };
     }
   }
@@ -625,8 +625,8 @@ export class ContentScanner {
       return sample.toString('utf8')
         .replace(/[\x00-\x09\x0B-\x1F\x7F-\x9F]/g, '') // Remove control chars
         .replace(/\uFFFD/g, ''); // Remove replacement char
-    } catch (error) {
-      logger.log('warn', `Error extracting text from buffer: ${error.message}`);
+    } catch (error: unknown) {
+      logger.log('warn', `Error extracting text from buffer: ${(error as Error).message}`);
       return '';
     }
   }
@@ -699,10 +699,10 @@ export class ContentScanner {
         subject: email.subject
       },
       success: false,
-      domain: email.getFromDomain()
+      domain: email.getFromDomain() ?? undefined
     });
   }
-  
+
   /**
    * Log a threat finding to the security logger
    * @param email The email containing the threat
@@ -722,10 +722,10 @@ export class ContentScanner {
         subject: email.subject
       },
       success: false,
-      domain: email.getFromDomain()
+      domain: email.getFromDomain() ?? undefined
     });
   }
-  
+
   /**
    * Get threat level description based on score
    * @param score Threat score