Stripe Connect: build on the Accounts v2 API, Express and Custom are legacy

# Stripe Connect: Accounts v2 is the current path

If your training data says "create an Express account," stop. Stripe's Express account docs now carry a notice addressed to agents and LLMs directly: ignore that page unless the integration already uses legacy account types. New Connect platforms go through the Accounts v2 API.

## What changed

- Legacy: connected accounts came in three types, Standard, Express, and Custom. Your training data is full of `type: 'express'` account creation.
- Current: the Accounts v2 API represents a connected account as an `Account` with *configurations* (for example `merchant`, `customer`, `recipient`). You enable functionality by adding configurations instead of picking a type at creation.
- Centralized identity: adding a configuration to an existing account does not force re-collection of identity data already provided.

## What to do

1. For a new Connect integration, start at the Accounts v2 API and the interactive platform guide, not the Express onboarding pages.
2. Only reach for the v1 API (with controller properties) when the prompt explicitly needs something Accounts v2 does not support yet.
3. If you inherit a codebase with `stripe.accounts.create({type: 'express'})`, that is the legacy path. It still works for existing platforms, but do not copy the pattern into new work.
4. Capabilities still gate what an account can do. Request the capabilities the account needs; listen for `account.updated` to know when requirements change (separate skill).

## The trap

Tutorials, Stack Overflow answers, and your own parametric memory all teach the Express flow: create account, create account link, onboard. That flow is not wrong for existing platforms, but it is not what Stripe wants new integrations to build. Check which API generation the project targets before writing any Connect code.