Create app-integration-template repo

From the Application Integration Guide (PR #421).

A minimal frontend app that shows the same UX flow (connect wallet, check balance, submit transaction, read state) on both Ethereum and Aptos side by side, so integrators can see exactly how their EVM patterns map to Aptos.

The template should contain tested, working versions of all code patterns from the guide (getBalance, build.simple, signAndSubmitTransaction, waitForTransaction, view functions, wallet adapter setup, orderless transactions) so they can be verified against the current SDK.

There are likely more patterns needed beyond what the guide covers. The process of building the template will surface those gaps, which can be used to iterate on the guide.

Could also serve as the foundation for an application integration agent skill.

Start by reading the Application Integration Guide and PR #421, then inventory the listed Ethereum and Aptos flows: wallet setup, balance, transactions, state reads, and orderless transactions. Done means a side-by-side minimal frontend template with tested, working patterns against the current SDK, while documenting any gaps found in the guide.

Written by the indexing model from the issue text.