Per-expiry IV / skew / PCR / OI / GEX (with OPEX enrichment)

One row per active expiry with the metrics most useful for chain-wide screening:

Pre-computed every 30s — ATM IV, 25Δ skew, put/call 25Δ IVs, PCR, call/put/total OI, net GEX.

Added by v2 (OPEX enrichment, on-the-fly):

• type — daily | weekly | monthly | quarterly (Deribit token parsed; quarterlies are last Fridays of Mar/Jun/Sep/Dec).
• is_anchor — true for monthly + quarterly anchors.
• expiry_date — ISO date when the token parses cleanly.
• notional_oi_usd — total_oi × spot_price (each contract is 1 unit of underlying on Deribit-style chains).
• max_pain — {strike, value} from a per-expiry max-pain pass over the latest chain snapshot. Cached 30s, shared with /v2/gex/max-pain and /v2/options/opex.