[Epic] Improve Importer Reliability and Resilience

[paralta]

Problem Statement

The importer pipeline has been a recurring source of breakages due to insufficient test coverage, significant rate limiting, and sensitive third-party dependencies.

Proposed Solution

This epic covers adding meaningful E2E tests (#1162), implementing proper rate limiting (#994), and resolving mcphost library instability (#1053) to reduce incidents and improve long-term maintainability.

Alternatives Considered

No response

Additional Context

No response

Checklist

• I have read the contributing guidelines
• I have verified this does not duplicate an existing feature request