Add StockWaves and 402Sentinel to First-Party services

[kaditang]

Two live, MPP-accepting services for the First-Party list:

• StockWaves — China & global market data, cross-asset quant signals, and a tokenized-stock pre-trade safety gate for AI agents. The flagship cross-asset decision brief accepts native MPP (mppx evm charge) alongside x402; settles USDC on Base.
• 402Sentinel — pre-payment counterparty-risk + buyer-side payment firewall + OFAC/FATF compliance + tokenized-RWA token safety checks for agent payments. The risk gate accepts native MPP alongside x402; settles USDC on Base.

Both are live and accepting MPP payments today (verified end-to-end: the 402 advertises a www-authenticate: Payment challenge and settles via the Coinbase/CDP facilitator). Entries added to the bottom of the First-Party section; [Name](URL) - Description. format.