Add Yeetful to your Coinbase agent with one prompt

Add Yeetful spend-controlled x402 payments to this agent project.

Yeetful gives an agent an "expense account": an allowlist of hosts plus
per-call/per-day USDC budgets, enforced locally BEFORE any payment is
signed, with a receipt for every decision. Docs: https://yeetful.com/docs

Do the following, asking me to confirm anything ambiguous:

1. Install: npm install yeetful viem (or the pnpm/yarn equivalent this
   repo already uses).

2. Find where this project makes HTTP calls to paid or x402 APIs. Create a
   single shared payer in src/lib/pay.ts (adjust path to repo conventions):

   import { yeetful } from 'yeetful/agent'
   import { createWalletClient, http } from 'viem'
   import { base } from 'viem/chains'
   import { privateKeyToAccount } from 'viem/accounts'

   const wallet = createWalletClient({
     // If this project already has a Coinbase Developer Platform (CDP)
     // wallet or another viem account, use THAT as the account instead.
     account: privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`),
     chain: base,
     transport: http(),
   })

   export const pay = yeetful({
     wallet,
     grant: {
       id: process.env.YEETFUL_GRANT_ID,
       allow: [], // TODO: add the exact hostnames this agent may pay
       perCallUsd: 0.05,
       perDayUsd: 2,
     },
     apiKey: process.env.YEETFUL_API_KEY,
     // www origin on purpose: fetch drops auth headers on cross-origin
     // redirects, and the apex currently redirects to www.
     ledgerUrl: 'https://www.yeetful.com',
     onEvent: (m) => console.log('[yeetful]', m),
   })

   Replace direct fetch calls to those paid hosts with pay(), and add each
   host to the grant's allow list. Call await pay.flushLedger() before
   short-lived scripts exit.

3. Env setup: add PRIVATE_KEY (or wire the existing CDP signer),
   YEETFUL_API_KEY, and YEETFUL_GRANT_ID to .env; make sure .env is
   gitignored; add the three keys to .env.example with placeholder values.

4. Now walk me through the two Yeetful dashboard steps INTERACTIVELY —
   one at a time, waiting for me to confirm each before continuing:
   a. Tell me to open https://yeetful.com/dashboard/keys, connect my
      wallet, sign in, and mint an API key. Remind me the yf_ secret is
      shown only once. Wait for me to paste nothing — I'll put it in .env
      myself — then continue when I say done.
   b. Tell me to copy YEETFUL_GRANT_ID from the "Your expense account"
      chip on that same page into .env, and to flip ON the agents I trust
      at https://yeetful.com/dashboard/approvals. Continue when I say done.

5. Verify without spending: run the agent against one free (non-402)
   allowlisted endpoint, confirm a $0 "settled" receipt logs and a ledger
   sync POST succeeds (no 401s). Show me the output. Do NOT make a paid
   call unless I explicitly say so.

Keep the caps small. Never print or commit secrets. If this repo's paid
hosts speak x402 v1 or v2, no extra handling is needed — the SDK detects
the protocol version per challenge.