feat(server): meter AI point usage across tenant AI features

Adds an ai_point_usage_logs ledger and a reserve/refund/complete pipeline
that charges AI points for article selection optimize, template analyze
/title/outline, and KOL prompt generate/optimize. Pending reservations
are reconciled when the kol-assist worker and template-assist tasks
finish or fail, so points refund automatically on errors. Workspace now
exposes the AI quota status and a paginated usage ledger.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/domain/workspace.go

@@ -23,12 +23,17 @@ type RecentArticle struct {
 }
 
 type QuotaSummary struct {
-	PlanCode   string     `json:"plan_code"`
-	PlanName   string     `json:"plan_name"`
-	TotalQuota int        `json:"total_quota"`
-	UsedQuota  int        `json:"used_quota"`
-	Balance    int        `json:"balance"`
-	ResetAt    *time.Time `json:"reset_at"`
+	PlanCode         string     `json:"plan_code"`
+	PlanName         string     `json:"plan_name"`
+	TotalQuota       int        `json:"total_quota"`
+	UsedQuota        int        `json:"used_quota"`
+	Balance          int        `json:"balance"`
+	ResetAt          *time.Time `json:"reset_at"`
+	AIPointsTotal    int        `json:"ai_points_total"`
+	AIPointsUsed     int        `json:"ai_points_used"`
+	AIPointsBalance  int        `json:"ai_points_balance"`
+	AIPointBaseChars int        `json:"ai_point_base_chars"`
+	AIPointsResetAt  *time.Time `json:"ai_points_reset_at"`
 }
 
 type KolWorkspaceCard struct {
@@ -41,3 +46,26 @@ type KolWorkspaceCard struct {
 	PackageCover         *string   `json:"package_cover"`
 	KolDisplayName       string    `json:"kol_display_name"`
 }
+
+type AIPointUsageLog struct {
+	ID           int64      `json:"id"`
+	UsageType    string     `json:"usage_type"`
+	ResourceType *string    `json:"resource_type"`
+	ResourceID   *int64     `json:"resource_id"`
+	ResourceUID  *string    `json:"resource_uid"`
+	RequestChars int        `json:"request_chars"`
+	BaseChars    int        `json:"base_chars"`
+	Points       int        `json:"points"`
+	Status       string     `json:"status"`
+	Model        *string    `json:"model"`
+	ErrorMessage *string    `json:"error_message"`
+	CompletedAt  *time.Time `json:"completed_at"`
+	CreatedAt    time.Time  `json:"created_at"`
+}
+
+type AIPointUsageListResponse struct {
+	Items    []AIPointUsageLog `json:"items"`
+	Total    int64             `json:"total"`
+	Page     int               `json:"page"`
+	PageSize int               `json:"page_size"`
+}