Add demo for OID4VP In-Task Auth Extension

[AlexanderShenshin]

Description

This PR adds a demo for experimental OID4VP In-Task Authorization Extension.

We have a basic sample in extension repo itself, but we also would like to add a more comprehensive demo/sample here for better discoverability.

[gemini-code-assist]

Code Review

This pull request introduces the OID4VP In-Task Authorization Extension — Partner Discount Vouchers Demo, which showcases an Agent-to-Agent (A2A) protocol integration with OID4VP using Genkit, OpenAI, and OWF Credo. Feedback on the implementation highlights a potential unhandled promise rejection in the merchant's asynchronous event listener onVerificationStateChanged if presentation evaluation fails. It is recommended to wrap this call in a try/catch block to handle errors gracefully and prevent process crashes or hanging waiters.

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[gemini-code-assist]

The onVerificationStateChanged method is an asynchronous event listener. If evaluatePresentation throws an error (for example, if getVerifiedAuthorizationResponse fails), the promise will reject, resulting in an unhandled promise rejection. This can crash the process or leave the waiter hanging until the timeout.\n\nWrapping the call in a try/catch block ensures that any verification errors are caught, logged, and resolved gracefully, allowing the waiter to be notified immediately instead of waiting for the full timeout.

  private async onVerificationStateChanged(event: OpenId4VcVerificationSessionStateChangedEvent): Promise<void> {\n    const { verificationSession } = event.payload\n    if (verificationSession.state !== OpenId4VcVerificationSessionState.ResponseVerified) return\n\n    const contextId = verificationSession.getTag('contextId') as string | undefined\n    if (!contextId) return\n\n    let result: AuthResult\n    try {\n      result = await this.evaluatePresentation(verificationSession.id)\n    } catch (error) {\n      console.error('[Merchant] Error evaluating presentation:', error)\n      result = { approved: false, reason: error instanceof Error ? error.message : 'verification failed' }\n    }\n\n    this.authResults.set(contextId, result)\n\n    const waiter = this.authWaiters.get(contextId)\n    if (waiter) {\n      this.authWaiters.delete(contextId)\n      waiter(result)\n    }\n  }