List PolyPay deposit endpoint on x402 discovery layers (agentic.market + pay.sh)

[Huygon764]

Problem:
PolyPay's x402 deposit endpoint is not listed on any agent-discoverable catalog. To make it discoverable on both pay.sh (Solana Foundation aggregator, sources from PayAI) and agentic.market (Coinbase, sources from CDP), we need to route settlements through both facilitators.

• PayAI stays default for UI deposit and docs — better rate limits, simple auth.
• Coinbase CDP path exists only for agentic.market visibility — requires Ed25519 JWT signed per-request (2-min TTL).
• CDP requires declareDiscoveryExtension metadata to index. PayAI requires discoverable: true flag.
• Indexing only happens after a successful settlement, so a real on-chain USDC deposit is needed to bootstrap.

Expectation:

• Two endpoints: /x402/deposit/:multisig (PayAI, default) and /x402/bazaar/deposit/:multisig (CDP).
• CDP path enables automatically when CDP_API_KEY_ID env is present.
• @coinbase/x402 SDK used for CDP JWT signing.
• CLI script scripts/bazaar-bootstrap.ts to perform the first settlement.
• After Base Sepolia bootstrap, listing visible at GET https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources.
• After Base mainnet bootstrap, listing visible on agentic.market and pay.sh.
• No UI change.