fix(web): verify MetaMask chain switch

[dirtybits]

Summary

• explicitly request Base Sepolia again after wallet_addEthereumChain, because EIP-3085 does not require adding a chain to make it active
• re-read eth_chainId after each requested switch and fail closed unless MetaMask reports Base Sepolia
• add behavioral regressions for the add-then-switch flow and a provider that reports success without changing chains

Test plan

• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism __tests__/lib/baseInjectedWallet.test.ts
• npm run format:check
• npm run lint --workspace @agentvouch/web
• npm run typecheck --workspace @agentvouch/web
• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism
• npm run verify:chain-map
• npm exec --workspace @agentvouch/web -- next build --webpack
• git diff --check origin/main...HEAD

Not verified

• No browser or live MetaMask/Base Sepolia transaction was run; the wallet RPC sequencing is covered by isolated behavioral tests.

[qodo-code-review]

ⓘ Qodo reviews are paused because your trial has ended. Ask your workspace admin to add credits to resume reviews. Manage billing