test: expand Core 2.0 conformance pack edge cases

[DigiEmu]

Summary

This PR expands the Core 2.0 conformance pack from 3 to 10 cases with additional negative and edge-case scenarios.

The goal is to increase confidence in the experimental conformance path, JSON report output, CI validation, and partner-facing test coverage.

Added

New conformance cases under testdata/core_2_conformance/:

• missing_required_field_error
• malformed_json_error
• unknown_reason_code_error
• unsupported_hash_algorithm_error
• wrong_profile_fail
• inside_payload_mutation_detected
• outside_metadata_ignored

Updated

• .github/workflows/ci.yml
• README.md
• cmd/digiemu/experimental_json_test.go
• internal/schema/conformance_report_schema_test.go
• internal/schema/verify_result_v2_schema_test.go
• testdata/core_2_conformance/report_expected_basic.json
• Core 2.0 documentation references and expected totals

New Expected Result

The experimental conformance CLI now reports:

Conformance run summary: total=10 passed=10 failed=0

The JSON report now includes:

{
  "status": "PASS",
  "total": 10,
  "passed": 10,
  "failed": 0
}

Notes

The current conformance runner validates expected verify-result documents structurally. Some new cases are representative partner test vectors for expected implementation behavior, not full runtime verification semantics yet.

UNKNOWN_REASON_CODE was not added because the current schema only allows enumerated reason codes. The corresponding case uses a schema-compatible INTERNAL_ERROR mapping.

Validation

• go test ./... passes
• experimental conformance CLI passes
• experimental conformance CLI --json passes

Compatibility

• No stable v1.0 behavior changed
• No snapshot hash behavior changed
• No CLI promotion to stable
• No HTTP API server implemented
• No signing, authentication, tenancy, policy judgement, or key custody added