fix: add non-null assertion to config.service loadConfig

Add non-null assertion operator to fix TypeScript error TS2322.
After assigning the config from response.json(), TypeScript still
considers it possibly null. The assertion is safe since we just
assigned it.

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

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

Author: klagrida

frontend/src/app/services/config.service.ts

@@ -24,7 +24,7 @@ export class ConfigService {
     }
 
     this.config = await response.json();
-    return this.config;
+    return this.config!;
   }
 
   getConfig(): AppConfig {