fix(secops-soar): improve error handling, marketplace imports, and packaging sync

[dandye]

Summary

This PR addresses multiple stability, diagnostic, and packaging issues across server/secops-soar:

1. Structured Exception Hierarchy & Clean Error Propagation:

   • Introduces typed exceptions in secops_soar_mcp/exceptions.py: SoarError, SoarConnectionError, SoarSSLError, SoarAuthError, and SoarHttpError.
   • HttpClient detects underlying SSL/TLS failures (walking the exception cause chain via is_ssl_cert_verification_error) and raises SoarSSLError, SoarAuthError, or SoarConnectionError directly.
   • Eliminates mutable state/side-channels (self.last_error) on the asynchronous client.

2. Actionable macOS TLS / certifi Error Handling:

   • bindings._get_valid_scopes() catches SoarSSLError during startup and provides clear guidance for macOS python.org installer users (/Applications/Python 3.X/Install Certificates.command or SSL_CERT_FILE=$(python -m certifi)).
   • Distinguishes TLS certificate failures from authentication errors (401/403) and network connection drops.

3. Dynamic Marketplace Module Import Resolution (Fixes [secops-soar] Dynamic marketplace tool import fails with ModuleNotFoundError when running installed package #293):

   • Updates secops_soar_mcp/server.py to resolve marketplace integration tools via secops_soar_mcp.marketplace.{module_stem} with fallback to marketplace.{module_stem}, preventing ModuleNotFoundError when the server is installed as a package.

4. Synchronize python-dotenv in setup.py (Fixes [secops-soar] setup.py is missing python-dotenv dependency from install_requires #294):

   • Adds "python-dotenv>=1.0.0" to install_requires in server/secops-soar/setup.py to match pyproject.toml.

5. Hermetic Unit Tests:

   • Adds 6 unit tests in tests/test_soar_unit.py covering SSL error detection, auth error translation, diagnostic message formatting, and marketplace path resolution.
   • Removes autouse=True from tests/conftest.py so unit tests can run hermetically without requiring live credentials in config.json.

Fixes #293
Fixes #294

Tests Run

• uv run --with "mcp<2" --with pytest --with pytest-asyncio --with aiohttp --with python-dotenv pytest tests/test_soar_unit.py (6 passed)