refactor: use the SDK custody client

[TaprootFreak]

Consumer side of step 4 of DFXswiss/packages#198: use the custody client from @dfx.swiss/react
and drop the local copies.

Depends on DFXswiss/packages#202.

Changes

• src/dto/safe.dto.ts and src/dto/order.dto.ts keep only what is local: the screen's operation
  enums (SafeOperationType, TransactionMode, TransactionType, FiatCurrency), the staff
  CustodyOrderListEntry, and ExchangeRate. Every wire type now comes from the package;
  OrderPaymentData and OrderPaymentInfo are CustodyOrderPaymentInfo and CustodyOrder there.
• useSafe calls useCustody() instead of building URLs by hand. The screen state — loading flags,
  request generations, account selection, asset pairing, the PDF download to disk — stays here.
• accountPath() is gone: toCustodyAccountId(account) from the package resolves the legacy
  account's null id.

What the corrected types surfaced

Three requests that the API would have rejected are now impossible to build:

• Orders sent the session token when the custody token was missing. The package requires the
  custody token, so custodyToken() fails here instead of the request failing there.
• Swap, withdrawal and send passed both amounts as number | undefined. The API prices from one
  side or the other and rejects a request carrying both or neither. orderAmount() decides which one
  goes out and refuses when there is none.
• A withdrawal passed data.bankAccount?.iban, which the API requires. It is now checked before
  the request.

isOwnAccount reads account.isOwner instead of inferring ownership from the presence of an owner
relation — the comment there asked for exactly that once the API exposed the flag. It does.

Before this can go green

The package pin in package.json still points at the published @dfx.swiss/react. CI stays red
until DFXswiss/packages#202 is merged and published and the pin is raised here. Verified locally
against a build of that branch: tsc clean, npm run lint clean, full suite at 673 passing with no
new failures (the two suites failing on develop today still fail, unchanged).

[github-actions]

🤖 PR Review Bot

❌ TypeScript: 40 errors

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