Generalize rejected data schema for confirmation responses

[andreabadesso]

Context

In PR #43, a rejectedDataSchema is introduced inline:

const rejectedDataSchema = z.object({ accepted: z.literal(false) });

This { accepted: false } pattern is already used across multiple response types in packages/hathor-rpc-handler/src/types/prompt.ts:

• SendNanoContractTxConfirmationResponse (line 242)
• CreateTokenConfirmationResponse (line 252)
• PinRequestResponse (line 262)
• CreateNanoContractCreateTokenTxConfirmationResponse (line 336)
• SendTransactionConfirmationResponse (line 314, uses accepted: boolean — slight variation)

And the rejection check (if (!response.data.accepted)) is repeated across all RPC methods:

• sendTransaction.ts
• sendNanoContractTx.ts
• createToken.ts
• createNanoContractCreateTokenTx.ts
• signWithAddress.ts
• signOracleData.ts

Proposal

Create a shared schema (e.g. in a schemas/ or validators/ file) that can be reused:

1. A shared rejectedDataSchema:

   export const rejectedDataSchema = z.object({ accepted: z.literal(false) });

2. Optionally, a discriminated union factory for confirmation responses:

   export const confirmationResponseSchema = <T extends z.ZodRawShape>(acceptedFields: T) =>
     z.discriminatedUnion('accepted', [
       z.object({ accepted: z.literal(true), ...acceptedFields }),
       rejectedDataSchema,
     ]);

This would standardize validation across all confirmation response handlers and reduce duplication.