feat(plugins): generate customer HTTP bundles

[pmasiphelps]

Summary

• generate a customer-specific Codex and Claude marketplace bundle for a fixed Streamable HTTP endpoint
• include the shared Dataiku skills without copying server configuration or credentials
• require interactive OAuth for plugin bundles and direct bearer deployments to managed MCP configuration
• document the supported Codex and Claude distribution surfaces

This PR is stacked on #155, which is itself stacked on #125.

Validation

• uv run pytest tests/test_http_plugin_bundle.py tests/test_plugin_packaging.py
• Codex plugin validator
• claude plugin validate
• full repository suite and pre-commit hooks passed on the combined change before splitting