Implement LLM provider configuration and update user settings

- Added functionality to update the default LLM provider for users via a new endpoint in UserController.
- Introduced LlmProvider enum to manage available LLM options: Auto, Gemini, OpenAI, and Claude.
- Updated User and UserEntity models to include DefaultLlmProvider property.
- Enhanced database context and migrations to support the new LLM provider configuration.
- Integrated LLM services into the application bootstrap for dependency injection.
- Updated TypeScript API client to include methods for managing LLM providers and chat requests.

src/Managing.Api/appsettings.json

@@ -9,8 +9,6 @@
       }
     }
   },
-
-
   "InfluxDb": {
     "Organization": "managing-org"
   },
@@ -28,6 +26,17 @@
   "Flagsmith": {
     "ApiUrl": "https://flag.kaigen.ai/api/v1/"
   },
+  "Llm": {
+    "Gemini": {
+      "DefaultModel": "gemini-2.0-flash"
+    },
+    "OpenAI": {
+      "DefaultModel": "gpt-4o"
+    },
+    "Claude": {
+      "DefaultModel": "claude-haiku-4-5-20251001"
+    }
+  },
   "N8n": {
   },
   "Sentry": {