pi-neuralwatt v0.15.4

45373d6: Take flex model pricing from the API’s already-discounted values instead of applying a local 0.65 multiplier at catalog build time.
48b331e: Sync the offline fallback model table with the live Neuralwatt API: remove GLM-5.2 and its variants (gone upstream), add glm-5.3-flash(-flex) and qwen-3.8-27b(-flex), and add flex variants for glm-5.3 and qwen3.6-35b.
db99586: Type the new service_tier, flex_discount_multiplier (models) and legacy_credits_usd, new_credits_usd (quota balance) API fields.
96b01f4: Resolve the overage billing rate from the subscription plan and billing interval (per-plan $7.00–$8.50/kWh, $10/kWh pay-as-you-go, Standard monthly rate as fallback) instead of a flat $5/kWh.