Add xero accounts create command and enhance accounts list/update

[thomasfedb]

Adds xero accounts create command, consistent with existing create commands (invoices, contacts, items, etc.)

• Supports flags: --name, --code, --type, --description, --tax-type, --enable-payments-to-account, --show-in-expense-claims, --add-to-watchlist
• Also accepts --file for JSON input
• Adds accountCreateSchema to validators

Also enhances existing accounts commands:

• accounts list now shows Tax Type and Description columns
• accounts update gains --show-in-expense-claims and --add-to-watchlist flags (also added to accountUpdateSchema)

Generated with Claude Code and checked by human