Handles Dispute resource endpoints.

Endpoints

• GET /v1/disputes/:id - Retrieve dispute
• POST /v1/disputes/:id - Update dispute
• GET /v1/disputes - List disputes

Note: Disputes cannot be created or deleted (created by card networks, immutable).

Dispute Object

%{
  id: "dp_...",
  object: "dispute",
  created: 1234567890,
  amount: 2000,  # $20.00 in cents
  charge: "ch_...",
  currency: "usd",
  status: "warning_needs_response" | "warning_under_review" | "warning_closed" |
          "needs_response" | "under_review" | "charge_refunded" | "won" | "lost",
  reason: "duplicate" | "fraudulent" | "subscription_canceled" |
          "product_unacceptable" | "product_not_received" | "unrecognized" |
          "credit_not_processed" | "general",
  evidence: %{},
  metadata: %{},
  # ... other fields
}