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/cmd/kol-assist-worker/main.go

@@ -27,10 +27,12 @@ func main() {
 	defer cancel()
 
 	assistworker.NewKolAssistWorker(
+		app.DB,
 		app.RabbitMQ,
 		app.KolAssists,
 		app.LLM,
 		app.Logger,
+		app.Cache,
 		app.Config.Generation.WorkerConcurrency,
 		app.Config.Generation.ArticleTimeout,
 	).Start(ctx)