Document and test MCP proxy support end to end

[davidruzicka]

Summary

Document and test MCP proxy support end to end across configuration loading, upstream session lifecycle, notification forwarding, and security boundaries.

Why

This feature touches configuration, transport behavior, and security-sensitive boundaries. It should land with production-oriented tests and user documentation instead of relying on follow-up cleanup.

Deliverables

• Add unit and integration tests for config validation, provider wiring, remote session lifecycle, and notification forwarding.
• Add security-focused tests for invalid auth combinations, tool filtering, SSRF rejection, and stdio gating.
• Update README.md, docs/PROFILE-GUIDE.md, and transport docs with setup and operational notes.
• Update IMPLEMENTATION.md if the architecture changes materially.
• Update CHANGELOG.md once implementation lands.

Acceptance criteria

• The implementation is covered by success and failure-path tests.
• Documentation explains remote HTTP first and stdio as optional/experimental.
• Operational limits and trust boundaries are documented clearly.

Suggested files

• README.md
• docs/PROFILE-GUIDE.md
• docs/HTTP-TRANSPORT.md
• IMPLEMENTATION.md
• test files under src/ and tests/

Agent-authored issue.

[github-actions]

🤖 Agent note (proposal-intake)

Resolution: create-fresh
Reason: no relevant existing issue or pull request matches this proposal
Linked issue: #220 (#220)