task: fix the fee abstraction examples (adapter vs token address, decimals, imports) #2362

Follow-up from #2257, which added a troubleshooting section to the fee abstraction guide but left the existing examples as they were.

What needs to be done?

Three problems in build-on-celo/fee-abstraction/using-fee-abstraction.mdx, found while checking the page against the fee currency list and the JSON-RPC behaviour on Celo mainnet. AGENTS.md section 5 says every example that stays must run.

1. CLI USDC example uses the adapter as the token. The first celocli transfer:erc20 block passes --erc20Address 0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B. That address is the USDC adapter; the USDC token is 0xcebA9300f2b948710d2653dD7B07f33A8B32118C (see Fee currency contracts). The text under the block says transfers use the token address. The USD₮ example below it is correct (token in --erc20Address, adapter in --gasCurrency).
2. viem step 3 mixes decimals and has missing imports. parseEther("1") - transactionFee treats USDC as 18 decimals, but USDC has 6; the snippet uses encodeFunctionData, parseEther and formatEther without importing them; step 1 calls hexToBigInt on the result of estimateGas, which viem already returns as a bigint.
3. Addresses are not labelled. Every address in the examples should carry the network name and, for tokens, the decimals (AGENTS.md section 5), for example // Celo mainnet (42220), USDC adapter.

Definition of done

• The CLI USDC example uses the token address for --erc20Address and the adapter for --gasCurrency, and the command is run once with its output noted in the PR
• The viem examples are self-contained (imports shown), use the token's decimals, and are run against Celo Sepolia with the command and output noted in the PR
• Every address in both examples is labelled with network and decimals
• mint broken-links green

Priority

medium

Size

S — hours

Refs #2257.