Type Alias Tier

Tier:
    | "free"
    | "intro"
    | "basic"
    | "pro"
    | "max"

Billing system types for SmartChats.ai

These types are the canonical definitions used across:

ts_common/apis/billing (credit math)
ts_node/apis/llm_service (provider handlers)
apps/firebase/functions (Cloud Functions + Firestore)
apps/smartchats (frontend display)