fix(fee-abstraction): correct the Celo Sepolia USDC token and adapter addresses

[GigaHierz]

The hole, and the fix

The Celo Sepolia USDC row on two guide pages was wrong in both columns:

	was	is
Token	0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B — the mainnet USDC adapter; no code on Sepolia	0x01C5C0122039549AD1493B8220cABEdD739BC44E — symbol()=USDC, decimals()=6 on Sepolia
Adapter	0x4822e58de6f5e485eF90df51C41CE01721331dC0 — no code on Sepolia (an Alfajores-era address)	0xbf1441Ea57f43f35f713431001f35742c88071c7 — registered in the Sepolia FeeCurrencyDirectory; adaptedToken() → 0x01C5…BC44E

Files: build-on-celo/build-with-ai/overview.mdx:125 and build-on-celo/fee-abstraction/using-fee-abstraction.mdx:52. The canonical reference page tooling/contracts/fee-currencies.mdx:72 already had the correct pair; the guides had drifted from it. Explorer links switched to celo-sepolia.blockscout.com, the explorer the reference page and the network-overview page use for Sepolia.

What this does NOT do / residual risk

• Does not touch legacy/protocol/transaction/erc20-transaction-fees.mdx:47, which carries the same stale pair labelled Alfajores — that file is deleted by task: Remove the Legacy tab — migrate still-relevant L1 content to Learn/Operate, delete the rest #2254.
• Does not add a CI check that re-verifies addresses against the directory. The repo has no test harness for content; the check used below is a 20-line viem script and could join the orphan check proposed in task: Cleanup — delete _deprecated/, prune dead-end redirects, add an orphan-page check to CI #2252 — left as a note there, not done here.
• Mainnet rows were re-verified and unchanged.

Judgement calls

• "Sepolia" → "Celo Sepolia" in the network column of the overview table, matching the rest of the docs.
• Kept the two guide tables rather than replacing them with a link to the reference page; task: Fee abstraction — differentiate the guide, contract-reference and spec pages and make their relationship explicit #2257 decides that.

Issues

Closes #2268 — the wrong rows are replaced and every address in them was verified on-chain (below). The OPEN item in the issue (verify the adapter column) is resolved: the old adapter had no code; the new one is the directory's.

Stacking / conflicts

Branched off main, independent of my other open PRs. No other open PR touches these two lines.

Verification evidence

Read straight from the chain on 2026-08-21 (FeeCurrencyDirectory resolved via the registry at 0x…ce10, then getCurrencies() and adaptedToken() / symbol() / decimals() on each):

SEPOLIA FeeCurrencyDirectory 0x9212Fb72ae65367A7c887eC4Ad9bE310BAC611BF: 21 currencies
0xbf1441Ea57f43f35f713431001f35742c88071c7  ADAPTER for 0x01C5C0122039549AD1493B8220cABEdD739BC44E (USDC/6)
0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B  eth_getCode on Sepolia -> 0 bytes
0x4822e58de6f5e485eF90df51C41CE01721331dC0  eth_getCode on Sepolia -> 0 bytes

MAINNET FeeCurrencyDirectory 0x15F344b9E6c3Cb6F0376A36A64928b13F62C6276: 20 currencies
0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B  ADAPTER for 0xcebA9300f2b948710d2653dD7B07f33A8B32118C (USDC/6)   # mainnet rows unchanged, correct

$ grep -rn 'sepolia' --include='*.mdx' . | grep -v legacy | grep -i '0x2F25deB3\|0x4822e58d'
(none)
$ mint broken-links   # on 10ee5c58
success no broken links found

Remaining ops steps

• none

Checklist

• Title is the commit message I want on main
• Every address in the diff verified on-chain, not copied
• mint broken-links passes
• No secrets in the diff