* docs: add llms.txt intro page for AI agents (#256)

Add a GitBook-friendly page introducing PolyPay's llms.txt support so
non-technical readers can discover the feature and link AI agents to
the live playbook.

- New page docs/llms-txt-for-agents.md covering what llms.txt is, the
  live endpoint, the five integration flows it documents, two ways to
  wire an agent up, and compatibility notes.
- Add the page to docs/SUMMARY.md between x402 and Architecture.
- Fix stale api.polypay.xyz references in docs/x402-deposits.md to the
  real api.polypay.pro host.

* feat(x402): add Coinbase CDP bazaar deposit route for agentic.market listing (#260)

Adds a second x402 deposit endpoint /x402/bazaar/deposit/:multisig that
routes through Coinbase CDP facilitator instead of PayAI, so the resource
gets indexed in CDP discovery and surfaces on agentic.market.

The default /x402/deposit/:multisig path keeps using PayAI (better rate
limits, simpler auth) — no UI change. CDP path activates implicitly when
CDP_API_KEY_ID is set; otherwise it returns a clear config error.

CDP requires Ed25519 JWT signed per-request (2-min TTL), so the service
now lazy-imports @coinbase/x402 createAuthHeader to produce the
Authorization header. Payment requirements for the CDP path also embed a
declareDiscoveryExtension-shaped extensions.bazaar block (strict JSON
Schema), without which CDP would settle but not index.

Includes scripts/bazaar-bootstrap.ts to produce the first real settlement
that triggers CDP indexing — bootstrap must run against a deployed
backend (the resource URL ends up in the catalog).

Refs #259

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Co-authored-by: BoHsuu <115441679+Huygon764@users.noreply.github.com>

…ring

Add a Rust/WASM (Arbitrum Stylus) port of MetaMultiSigWallet and wire
Arbitrum Sepolia (421614) through shared, frontend and backend. The
contract is deployed and validated on-chain (Poseidon parity proven vs
the deployed PoseidonT3 library).

Per-account auto-deploy from the relayer is still open: the full contract
is ~29KB compressed, over the 24KB EVM limit, so cargo-stylus fragments
it and the single-bytecode StylusDeployer path can't be used. Options to
resume (proxy factory / CLI shell-out / manual) are documented in
packages/stylus/NOTES.md.

Wire Arbitrum Sepolia (421614) as a third destination chain alongside
Horizen and Base. Testnet only — zkVerify has no Arbitrum One verifier yet.

- Per-account multisig wallets via EIP-1167 proxy + shared Stylus impl,
  created on-chain by MetaMultiSigWalletStylusFactory.
- Stylus impl adds init() for the proxy pattern, plus an internal
  self-call dispatcher to work around the Stylus delegatecall + CALL
  msg.sender issue (see packages/stylus/NOTES.md).
- Custom 52-byte proxy variant of EIP-1167 that accepts plain ETH
  transfers (empty-calldata STOP) so cargo-stylus's fragmented loader
  doesn't revert deposits.
- Backend relayer routes Stylus-chain deploys through the factory;
  zkVerify aggregation domain 4 wired for chain 421614.
- Frontend network picker + sidebar surface Arbitrum Sepolia on testnet.
- Shared config carries impl/factory addresses + Circle USDC for 421614.
- Fix prisma findUnique by address_chainId in add/remove signer handlers
  (existing bug surfaced by the new chain).
- New docs/arbitrum-stylus.md user guide covering flows, limitations
  (add/remove signer broken, 6h aggregation cadence, MetaMask Blockaid
  warning) and on-chain addresses.