tokenized-stock-peg: spec validation fix + methodology hardening

[Flotapponnier]

Summary

• rank_matrix_query groups by asset which the validator rejects (must be provider); dropped, the field is optional (stablecoin-peg has none). This was blocking materialization, page 404ed on staging
• Reference candles 5m to 1m: cuts worst-case reference staleness from 5 min to 1 min during regular hours
• Methodology additions from self-review: the fee-band reading grid (a 2% pool 150bps off is at equilibrium, cross-symbol ranking partly reflects fee tiers) and the USDG quote-asset caveat (a peg wobble = correlated deviation across all symbols)