fix(207): align abstract/FAQ with tx_id methodology, fix Fomo wallet

[Flotapponnier]

Summary

• Fix abstract in solana-unique-traders.yml: was describing fee_payer from solana.transactions, now correctly describes COUNT(DISTINCT tx_id) from solana.account_activity with inflow filter
• Fix FAQ Q1 answer: was "distinct wallet addresses, a wallet trading 1000 times counts as 1", now correctly says tx_id proxy with 3-10x upward bias vs unique wallets
• Fix Fomo fee wallet in harness dune.go: HrTf9CzXR1dRH4Sof5QrpmGWwpwAf3qZzwCsEjQpXcSq → R4rNJHaffSUotNmqSKNEfDcJE8A7zJUkaoM5Jkd7cYX (verified against DeFiLlama dimension-adapters during bench 203 work)

Test plan

• YAML CI passes (no em-dashes, field lengths within limits)
• Fomo wallet shows activity in Dune (correct address is the USDC fee collector)