feat(error-handling): implement LLM error adaptation and classification for chat streaming

- Introduced LLMErrorCategory and adapt_llm_exception to normalize LLM exceptions.
- Updated llm_retryable_message and llm_permanent_message to utilize the new adaptation logic.
- Enhanced classify_stream_exception to classify provider errors and return user-friendly messages.
- Added tests for error classification and adaptation to ensure robustness.
- Updated frontend error handling to display appropriate messages based on new classifications.

surfsense_web/lib/chat/chat-request-errors.ts

@@ -91,6 +91,10 @@ export function tagPreAcceptSendFailure(error: unknown): unknown {
 			"TURN_CANCELLING",
 			"AUTH_EXPIRED",
 			"UNAUTHORIZED",
+			"MODEL_AUTH_FAILED",
+			"MODEL_NOT_FOUND",
+			"MODEL_CONTEXT_LIMIT",
+			"MODEL_PROVIDER_UNAVAILABLE",
 			"RATE_LIMITED",
 			"NETWORK_ERROR",
 			"STREAM_PARSE_ERROR",