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.

cmd/testdata/aiagent/init.go

@@ -87,6 +87,7 @@ func buildSeedItems(aiConfigID int64, knowledgeIDs []int64, defaultTeamIDs strin
 			ReplyTimeoutSeconds: 180,
 			TeamIDs:             defaultTeamIDs,
 			HandoffMode:         enums.AIAgentHandoffModeWaitPool,
+			FallbackMode:        enums.AIAgentFallbackModeSuggestRetry,
 			FallbackMessage:     "我暂时没有找到足够准确的信息。你可以补充具体的问题，我再继续帮你查。",
 			KnowledgeIDs:        utils.JoinInt64s(knowledgeIDs),
 			SkillIDs:            defaultSkillIDs,

cmd/testdata/kb/kb.go

@@ -118,7 +118,6 @@ func ensureKnowledgeBase(db *gorm.DB) (*models.KnowledgeBase, error) {
 			ChunkMaxTokens:        400,
 			ChunkOverlapTokens:    40,
 			AnswerMode:            int(enums.KnowledgeAnswerModeStrict),
-			FallbackMode:          int(enums.KnowledgeFallbackModeNoAnswer),
 			AuditFields: models.AuditFields{
 				CreatedAt:      now,
 				CreateUserID:   constants.SystemAuditUserID,
@@ -168,7 +167,6 @@ func ensureFAQKnowledgeBase(db *gorm.DB) (*models.KnowledgeBase, error) {
 			ChunkMaxTokens:        0,
 			ChunkOverlapTokens:    0,
 			AnswerMode:            int(enums.KnowledgeAnswerModeStrict),
-			FallbackMode:          int(enums.KnowledgeFallbackModeNoAnswer),
 			Remark:                "测试数据初始化自动生成",
 			AuditFields: models.AuditFields{
 				CreatedAt:      now,
@@ -197,7 +195,6 @@ func ensureFAQKnowledgeBase(db *gorm.DB) (*models.KnowledgeBase, error) {
 		"chunk_max_tokens":        0,
 		"chunk_overlap_tokens":    0,
 		"answer_mode":             int(enums.KnowledgeAnswerModeStrict),
-		"fallback_mode":           int(enums.KnowledgeFallbackModeNoAnswer),
 		"remark":                  "测试数据初始化自动生成",
 		"update_user_id":          constants.SystemAuditUserID,
 		"update_user_name":        constants.SystemAuditUserName,