Consume exported Sociosphere receipt input in validate_change stub

[mdheller]

Summary

Adds exported Sociosphere SVF receipt input support to the validate_change API stub.

Changes

• API stub reads exported_sociosphere_receipt from the request payload.
• verified receipts project to verified_receipt readiness.
• failed and stale receipts remain blocked.
• SVF run refs are kept in evidence_summary.run_refs, separate from AgentPlane sandbox_run_ref.
• API smoke validator now requires exported receipt support.
• Adds an exported Sociosphere receipt request fixture.

Refs #549

[mdheller]

Status note: PR currently has useful exported Sociosphere receipt input changes and negative failed/stale fixtures, but no GitHub Actions runs are visible for current head 96be79f314b6d5b6f2790c6499a7d6405f59cbcf through the connector.

I verified .github/workflows/validate-change-v2-api-stub.yml is configured for pull_request into main, so this appears to be delayed Actions scheduling or connector visibility rather than missing workflow configuration.

Holding merge until at least validate-change-v2-api-stub and ci are observable green.

[mdheller]

Updated PR after upstream Sociosphere export-manifest contract landed.

Upstream dependency now merged:

• Add SVF exported receipt manifest contract sociosphere#456 — Add SVF exported receipt manifest contract
• Merge SHA: 7133223edd7784a36b15e3eee9065f17b49b5451
• Manifest path: artifacts/svf/exports/latest/export-manifest.json

This PR now links the verified exported receipt request fixture to that upstream manifest through:

• sociosphere_refs.export_manifest_ref
• exported_sociosphere_receipt.export_manifest_ref

The smoke validator now requires the verified exported receipt fixture to point at the merged upstream manifest.

Current PR head: e8033945c0aa1071ff908ca4396a2a54c4d6c34f

CI remains not visible through the connector for this PR head, so merge remains held.