feat: add fallback mode for AI agents and update knowledge base handling

- Introduced AIAgentFallbackMode with options for NoAnswer and SuggestRetry.
- Updated AI agent edit component to include fallback mode selection.
- Modified API types and payloads to accommodate fallback mode.
- Removed deprecated KnowledgeFallbackMode and related logic from knowledge base.
- Adjusted knowledge retrieval and response handling to utilize new fallback logic.
- Updated tests to reflect changes in fallback mode handling for AI agents.

internal/ai/rag/answer_test.go

@@ -11,24 +11,19 @@ import (
 func TestBuildFallbackAnswer(t *testing.T) {
 	tests := []struct {
 		name     string
-		mode     enums.KnowledgeFallbackMode
+		mode     enums.AIAgentFallbackMode
 		expected string
 	}{
 		{
 			name:     "no answer",
-			mode:     enums.KnowledgeFallbackModeNoAnswer,
+			mode:     enums.AIAgentFallbackModeNoAnswer,
 			expected: "当前知识库暂无明确信息。",
 		},
 		{
 			name:     "suggest retry",
-			mode:     enums.KnowledgeFallbackModeSuggestRetry,
+			mode:     enums.AIAgentFallbackModeSuggestRetry,
 			expected: "当前知识库里没有找到足够明确的信息，你可以换个更具体的问法再试一次。",
 		},
-		{
-			name:     "transfer human",
-			mode:     enums.KnowledgeFallbackModeTransferHuman,
-			expected: "当前知识库里没有找到足够明确的信息，建议转人工进一步处理。",
-		},
 	}
 
 	for _, tt := range tests {