Whole-market spot meta + per-pair asset ctx (markPx / midPx / 24h) in one call

HL Info `spotMetaAndAssetCtxs` — one wallet-agnostic call returning `[spotMeta, spotAssetCtxs[]]`; the second element carries each spot pair's `markPx`/`midPx`/`prevDayPx`/volume, for valuing a whole wallet's spot holdings in ONE shot instead of N per-pair calls (QF-10938). Served from OFFICIAL behind a shared serve-stale cache — the self-hosted node can't serve complete spot prices, so this is the ONE place Artery keeps them, the SAME cache its own NAV valuation reads (a client and NAV always see one spot table). IMPORTANT: `assetCtxs[]` aligns to each pair's canonical `index`, NOT the `universe[]` array position — do NOT zip by array index (QF-10684).