Score history index: per-coin coverage, method versions, hash format

Score history: every recorded change to a coin's eight metric scores as a dated record with the TVR Score, the scoring method version, a source label (baseline for the opening record, auto_captured for rows written from the change itself), the public reason where one was recorded, and a SHA-256 hash of the record. Forward-only from the day the record began; nothing is reconstructed and no reason is invented. Free slice (the last 90 days or the last 3 records, whichever is longer) at GET https://truevaluerankings.com/api/history/{symbol} and in the MCP tool get_historical_scores. The full record is included with the Premium agent key (scope "full") and is sold per pull ($0.05, x402 or MPP, POST https://truevaluerankings.com/premium/score-history) only once a coin's record extends beyond the free slice; until then the request is refused before any payment and the free slice is the whole record.