feat(secops-soar): improve error message and docs for SOAR certifi issue

[s1v4-d]

Catch SSL certificate verification errors in the SOAR MCP server and display actionable error messages instead of the generic 'Failed to fetch valid scopes from SOAR' message.

• Add SoarSSLError and SoarConnectionError custom exceptions in http_client.py
• Add _is_cert_verify_error() helper that walks the exception cause chain
• Add _handle_ssl_error() to detect and re-raise SSL/connection errors with platform-aware fix instructions (macOS Install Certificates.command, pip install certifi)
• Update bindings.py and server.py to propagate and log specific error types
• Add SSL_CERTIFI_ERROR_MESSAGE, CONNECTION_ERROR_MESSAGE, and CREDENTIALS_ERROR_MESSAGE constants to consts.py
• Add Troubleshooting section to server/secops-soar/README.md
• Add SOAR SSL troubleshooting note to root README.md
• Add 20 unit tests covering all error paths (SSL cert verify, generic SSL, connection refused, bad credentials, message content quality)

Closes #191

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