`BazaRb#fee` has no idempotency badge, so a retried 5xx charges the user twice

[morphqdd]

fee posts to /account/fee through post (lib/baza-rb.rb:492), and post runs inside retry_on, which repeats the request on any 429 and any code above 499. A fee is money leaving the account, and nothing in the request lets the server recognise a repeat.

What happens: when a proxy answers 503 after the server has already booked the fee, the client books it again.

fee returned: 7
POSTs to /account/fee: 2
  #0: _csrf=tok&amount=1.500000&job=42&summary=coffee&tab=unknown
  #1: _csrf=tok&amount=1.500000&job=42&summary=coffee&tab=unknown
fee params:      [[:req, :tab], [:req, :amount], [:req, :summary], [:req, :job]]
transfer params: [[:req, :recipient], [:req, :amount], [:req, :summary], [:key, :job], [:key, :badge]]

transfer was given a badge: for exactly this in #423; fee never got one.

What should happen: fee should accept a badge: idempotency key the way transfer does and send it in the body, so the server can collapse a repeated charge.