Enhance smoking tracking features with AI next smoke time suggestions

- Added new API endpoint `GET /api/v1/smoke/next_smoke_time` to provide AI-generated suggestions for the next smoking time based on user data.
- Introduced a new database table `fa_smoke_ai_next_smoke` to store structured AI time node suggestions.
- Updated smoke handler and service to integrate the new AI next smoke time functionality.
- Enhanced documentation to reflect the new API endpoint and its usage, including details on how to generate AI time nodes.

internal/smoke/model/smoke_ai_next_smoke.go

@@ -0,0 +1,32 @@
+package model
+
+import "time"
+
+// SmokeAINextSmoke 对应表 fa_smoke_ai_next_smoke（AI 生成的“下次抽烟时间节点”）。
+//
+// 说明：
+// - 该表只保存“时间节点”本身（每个时间点一条记录），AI 元信息复用 fa_smoke_ai_advice（通过 AIAdviceID 关联）。
+// - 沿用旧系统字段（createtime/updatetime/deletetime 为秒级时间戳），不使用 gorm.Model。
+type SmokeAINextSmoke struct {
+	ID  uint `gorm:"primaryKey;autoIncrement;comment:记录ID" json:"id"`
+	UID int  `gorm:"column:uid;index:idx_smoke_ai_next_uid_date,priority:1;comment:用户ID" json:"-"`
+
+	PlanDate   time.Time `gorm:"column:plan_date;type:date;index:idx_smoke_ai_next_uid_date,priority:2;comment:计划日期(当天)" json:"plan_date"`
+	AIAdviceID uint      `gorm:"column:ai_advice_id;index:idx_smoke_ai_next_advice,priority:1;comment:关联AI建议ID(fa_smoke_ai_advice.id)" json:"ai_advice_id"`
+
+	// NodeType: not_before / suggested / node
+	NodeType string    `gorm:"column:node_type;size:20;index:idx_smoke_ai_next_advice,priority:2;uniqueIndex:uniq_smoke_ai_next_node,priority:2;comment:节点类型" json:"node_type"`
+	NodeAt   time.Time `gorm:"column:node_at;type:datetime;uniqueIndex:uniq_smoke_ai_next_node,priority:3;comment:时间点" json:"node_at"`
+
+	CreateTime *int64 `gorm:"column:createtime;comment:创建时间(秒)" json:"createtime,omitempty"`
+	UpdateTime *int64 `gorm:"column:updatetime;comment:更新时间(秒)" json:"updatetime,omitempty"`
+	DeleteTime *int64 `gorm:"column:deletetime;comment:删除时间(秒)" json:"deletetime,omitempty"`
+}
+
+func (SmokeAINextSmoke) TableName() string {
+	return "fa_smoke_ai_next_smoke"
+}
+
+func (SmokeAINextSmoke) TableComment() string {
+	return "AI下次抽烟时间节点"
+}