docs: add Core 2.0 Draft 2 review summary

[DigiEmu]

Summary

This PR adds a review summary for DigiEmu Core 2.0 Draft 2.

The document summarizes the review outcome for v2.0.0-draft.2, including confirmed strengths, known out-of-scope areas, and recommended next steps.

Added

• docs/CORE_2_DRAFT_2_REVIEW_SUMMARY.md

Updated

• docs/CORE_2_PARTNER_HANDOFF.md
• docs/CORE_2_STATUS.md
• docs/SPEC_INDEX_v1.0.md

Review Scope

The review summary covers:

• Core 2.0 conformance path
• experimental conformance CLI
• JSON conformance report
• conformance report schema
• OpenAPI contract draft
• Docker usage path
• Docker CI validation
• partner handoff readiness
• feedback intake process

Verdict

v2.0.0-draft.2 is ready for partner handoff as a draft milestone.

No critical blockers were identified.

Compatibility

• Documentation-only change
• No production code changed
• No CLI behavior changed
• No schemas changed
• No testdata changed
• No tag changes
• No v1.0 behavior changed
• Core 2.0 remains draft/pre-release unless explicitly marked stable

Validation

• go test ./... passes