refactor(web): remove dead Base approval branch

[dirtybits]

Summary

• remove the unreachable sequentialApproval option and sequential approval branch from Base passkey USDC pull-writes
• remove source-text assertions that only preserved the unreachable branch
• retain the existing batched exact-approval plus contract-call behavior for every caller

Test plan

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

Not verified

• No wallet/browser or live Base Sepolia transaction was run; this change only removes an unreachable internal path and does not alter the remaining batched write behavior.

[qodo-code-review]

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