feat(crypto): rewrite verifyAccess to support asymmetric E2EE signatures (#93)

[annukumar123]

🎯 Overview

This PR addresses Issue #93 by upgrading the verifyAccess pipeline in the SDK from a plain JSON pass-through to a secure, asymmetric End-to-End Encryption (E2EE) cryptographic verification protocol.

🛠️ Changes Implemented

• src/config-validation.mjs: Extended the client configuration validator schema to recognize and validate the optional, PEM-encoded privateKey property.
• src/client.mjs: Rewrote the verifyAccess method to check for a privateKey. If present, it wraps the options payload with an automated validation timestamp, signs it using Node's native crypto engine (RSA-PSS-SHA256), and securely structures the outbound body with encrypted_payload, signature, and algo keys.
• test/sdk.test.mjs: Added an isolated integration unit test suite that generates a mock RSA key pair to fully verify signature generation, cryptographic algorithm headers, and inner payload binding functionality.

🧪 Test Results

All 9 core tests and verification suites are passing successfully locally without errors:

✔ missing baseUrl throws (2.0578ms)
✔ capture posts to correct endpoint and fills defaults (43.4127ms)
✔ verifyAccess and runFeature post correctly (2.4922ms)
▶ UploadPanel E2EE Cryptographic Verification Suite (#93)
  ✔ verifyAccess generates cryptographic signature when privateKey configuration is set (249.8041ms)
✔ UploadPanel E2EE Cryptographic Verification Suite (#93) (250.2249ms)
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