Identity schema corrected for income bounds and "tax_id_type"

Broker API

The Identity schema now matches what the API actually returns:

• annual_income_min, annual_income_max, liquid_net_worth_min, liquid_net_worth_max, total_net_worth_min, and total_net_worth_max are documented as decimal strings (type: string, format: decimal), consistent with other monetary fields such as cash and buying_power. Examples have been added for each.
• tax_id_type is no longer unconditionally required and may be null on read. It is required on write only when tax_id is supplied; some accounts return identity data without it.

Affected Endpoints

• GET /v1/accounts
• POST /v1/accounts
• GET /v1/accounts/{account_id}
• PATCH /v1/accounts/{account_id}