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

ts/opsserver/handlers/radius.handler.ts

@@ -52,8 +52,8 @@ export class RadiusHandler {
           try {
             await radiusServer.addClient(dataArg.client);
             return { success: true };
-          } catch (error) {
-            return { success: false, message: error.message };
+          } catch (error: unknown) {
+            return { success: false, message: (error as Error).message };
           }
         }
       )
@@ -144,8 +144,8 @@ export class RadiusHandler {
                 updatedAt: mapping.updatedAt,
               },
             };
-          } catch (error) {
-            return { success: false, message: error.message };
+          } catch (error: unknown) {
+            return { success: false, message: (error as Error).message };
           }
         }
       )