docs(minipay+fee-abstraction): add USDT 6-decimal warning and USDT celocli transfer example

[samuelchimmy]

What changed

build-on-celo/build-on-minipay/code-library.mdx

• Added a <Warning> callout before the Request an ERC20 token transfer section explicitly stating that USDT and USDC use 6 decimals on Celo, not 18
• Updated the inline address comment in requestTransfer to include the decimal count next to each token address (USDm: 18, USDC: 6, USDT: 6)
• Corrected the parseUnits comment from "USDm (18), USDC (6)" — which omitted USDT entirely — to "USDm uses 18 decimals; USDC and USDT use 6 decimals"

build-on-celo/fee-abstraction/using-fee-abstraction.mdx

• The CLI section showed a USDC example only. Added an equivalent USDT celocli transfer:erc20 example using the correct USDT mainnet token address (0x48065fbbe25f71c9282ddf5e1cd6d6a887483d5e) and its fee adapter address (0x0e2a3e05bc9a16f5292a6170456a710cb89c6f72)
• Clarified that --value for both USDC and USDT is in units of 10^6

Why

The requestTransfer snippet listed USDT in the address comment but gave no decimal count for it, while explicitly noting USDC (6). A developer building a USDT transfer and following this example without noticing the omission would likely pass 18 as tokenDecimals, sending 1,000,000,000,000× the intended amount. The <Warning> and inline comment make the 6-decimal requirement impossible to miss.

The fee-abstraction CLI section documented USDC usage but left USDT as table-only — no runnable example. The USDT adapter address is already in the table above; adding the celocli example makes it consistent.

How to verify

1. In code-library.mdx: search for requestTransfer — confirm the <Warning> block appears above the code fence and the inline comment now reads (6 decimals) next to USDT
2. In using-fee-abstraction.mdx: search for 48065fbbe — confirm a complete celocli command appears using it as --erc20Address and 0e2a3e05 as --gasCurrency
3. Token addresses can be verified at celoscan.io/address/0x48065fbbe25f71c9282ddf5e1cd6d6a887483d5e and celoscan.io/address/0x0e2a3e05bc9a16f5292a6170456a710cb89c6f72

[GigaHierz]

Thanks for this fix, @samuelchimmy! Because our CI can't run on PRs from external forks, I've recreated your changes verbatim on an org-owned branch so they can be merged: #2196. Full credit to you in the new PR description.

Closing this in favor of #2196.